Amortization Calculator

The calculator above models how a fixed-rate loan balance declines over time through regular scheduled payments - and shows how each payment divides between interest and principal period by period. It extends what a basic payment calculator tells you (the payment amount) by showing where that payment goes across the entire loan life.

Use this tool to build an understanding of loan cost structure before you borrow - and to ask better questions when a lender provides an official schedule. It is not a lender's amortization table, a loan agreement, or a quote. All numbers produced by this calculator are estimates from the hypothetical inputs you enter.

Loans Plainly does not originate loans, provide lender quotes, or rank lenders. Nothing on this page is personalized financial advice.

What amortization means - a plain-language definition

Amortization is the process of paying down a loan balance over time through a series of scheduled payments. In a standard fixed-rate amortizing loan, the payment amount stays the same each period - but the way that payment divides between interest and principal shifts with every payment made.

The word comes from a Latin root meaning "to kill off" or "to extinguish." An amortizing loan is one that extinguishes itself through regular payments according to a defined schedule. At the end of the schedule, the balance reaches zero (or near zero, accounting for rounding).

Not all loans amortize in the standard way. Interest-only loans, balloon loans, and deferred-interest arrangements have different payoff structures. This calculator models standard fixed-rate amortization only.

Why amortization matters for borrowers: Because interest accrues on the outstanding balance, and the balance is highest at the beginning of the loan, more of each early payment goes toward interest rather than reducing what you owe. See the amortization glossary entry for definitions, a mortgage-style table example, and links to related guides. You are not building equity at the same pace throughout the loan - you build it slowly at first and faster near the end. Understanding this pattern helps you evaluate the real cost of borrowing, the effect of extra payments, and the tradeoffs between different loan terms.

Amortization schedule refers to the complete table showing every payment across the loan life, with the interest portion, principal portion, and remaining balance listed for each period. Your lender produces an official schedule based on your actual loan terms. This calculator produces an estimate based on the simplified inputs you enter.

Extra payments are amounts paid in addition to the scheduled regular payment. When applied to principal (rather than held and applied on the next due date), extra payments reduce the outstanding balance faster than the standard schedule - which reduces the interest that accrues in subsequent periods. The practical effect is that more of every future regular payment goes toward principal. See the limitations section for important caveats about how lenders actually apply prepayments.

What the inputs mean

Principal

The principal is the starting loan balance you want to model - the amount you are borrowing (or have borrowed) before any payments are made. Enter the amount you expect to finance, not the total of payments or any other figure.

For context on what principal means in the structure of a loan, see the principal glossary entry.

Annual rate (%)

The annual rate field accepts a nominal interest rate expressed as a percentage per year. The calculator divides this into a periodic rate based on your payment frequency. This is not a rate pulled from any lender, market data source, or your credit profile - it is a hypothetical input you supply.

To run a useful scenario, you need a rate estimate. Potential sources include rate ranges published by credit unions or banks (understanding these are starting points, not your personal offer) or a rate from a pre-approval you have received. Run multiple scenarios at different rates to see the sensitivity - the total interest difference between 7% and 9% over a long term can be thousands of dollars.

For the relationship between interest rate and APR, see the interest rate glossary entry and the APR glossary entry.

Term (months)

The term is the number of months in the loan. A 36-month term means 36 monthly payments over three years. A 60-month term means 60 payments over five years.

Longer terms produce lower regular payments and more total interest paid. Shorter terms do the reverse. The amortization schedule makes this tradeoff visible: a longer term means more periods during which interest accrues on an outstanding balance.

For a fuller explanation of how term affects total cost, see the loan term glossary entry.

Payment frequency

Payment frequency determines how many payment periods occur per year - monthly (12), biweekly (26), or weekly (52). More frequent payments mean more periods per year and slightly different per-period interest accrual.

Biweekly payments can reduce total interest compared to monthly payments on the same loan because more payments are made per year (26 biweekly payments vs. 12 monthly payments means effectively one extra full payment per year), which reduces the balance faster. The calculator models this difference through the period count and per-period rate.

Extra payment per month (optional)

An optional extra payment field accepts an additional dollar amount applied toward principal each period, on top of the regular scheduled payment. This does not change the regular payment calculation - it is applied in addition to it.

In the model, each extra payment reduces the principal before the next period's interest accrues, which reduces interest in subsequent periods. The cumulative effect across many periods is that total interest paid falls below the baseline.

Important: this model assumes the extra payment is applied immediately to principal. Real lenders may hold prepayments, apply them on specific dates, or require written instructions to apply them to principal rather than future scheduled payments. See the limitations section and the caution block below before assuming calculator results will match your lender's outcome.

What the outputs mean

Estimated total interest - The sum of all interest portions across every modeled payment period. This is the clearest single measure of what the financing costs, separate from repaying the principal itself.

Estimated total paid - The sum of all regular payments plus any extra payments across the full term. Subtracting the principal from this figure gives total interest.

Estimated remaining balance - The balance remaining after the final modeled period. In a correctly structured amortization, this should be near zero. A small residual (a few cents to a few dollars) may appear due to rounding in fixed-payment calculations.

Payment periods modeled - The total count of payment periods in the schedule. For a 48-month monthly loan, this is 48. For a 48-month biweekly loan, this is approximately 104.

First periods preview - A table showing the payment amount, interest portion, principal portion, and remaining balance for the early periods of the schedule. This preview illustrates the core amortization pattern - that early payments carry a high interest share and a low principal share.

How principal and interest split across the loan life

The defining feature of standard amortization is that the division of each payment shifts over time - but the total payment stays fixed. This is the pattern that makes early payoff and extra payments valuable and makes longer terms costly.

The mechanics: your periodic interest charge is the outstanding balance multiplied by the periodic rate. Early in the loan, the balance is at its maximum, so the interest charge is at its maximum. The remainder of the fixed payment covers principal. As the principal falls, the interest charge falls, and more of the fixed payment is available to cover principal. The process accelerates - falling balance means falling interest means faster principal reduction.

Hypothetical dollar example - $18,000 principal, 8% annual rate, 48-month term, monthly payments

The table below shows estimated principal and interest amounts at specific points in the payment schedule. All numbers are hypothetical and illustrative only. Run the calculator with your own inputs.

All figures above are hypothetical and rounded for illustration. Key observation: the interest portion in month 1 (~$120) is roughly 40 times the interest portion in month 48 (~$3). The same fixed payment covers far more principal by the end of the loan than at the beginning. This is why making extra payments early in a loan has a larger impact on total interest than making the same extra payments near the end.

Extra payment effects - what they actually do

Extra payments are the most practical lever an amortization calculator reveals. When you apply additional amounts to principal, the balance falls faster than the standard schedule, which reduces interest in every subsequent period. The earlier in the loan life you make extra payments, the more periods benefit from the reduced balance.

The extra payment field in this calculator lets you model a consistent monthly extra payment. In practice, borrowers may also make occasional lump-sum payments - a tax refund applied to the principal, for example. This calculator models recurring extra payments rather than one-time lump sums, but the directional logic is the same.

Extra payment scenario table (illustrative)

Hypothetical base: $20,000 principal, 7.5% annual rate, 60-month term, monthly payments

Numbers above are hypothetical and rounded for illustration. The pattern: each additional $100 per month in extra payments saves roughly $500-1,000 in estimated total interest in this scenario. The relationship is not perfectly linear because each extra dollar reduces the balance on which future interest accrues.

Note that the extra payment model in this calculator assumes the full term runs - meaning it shows reduced interest at each period but does not automatically truncate the schedule at an early payoff point. Your actual loan may pay off before the full term if extra payments are sufficient, which would further reduce total interest paid.

Four illustrative amortization scenarios

The following scenarios are hypothetical. They are designed to show how different borrowing and repayment decisions affect total interest over time - not to represent any real loan product or approval.

Scenario 1 - Short term vs. long term: the total interest difference made visible

A borrower needs $15,000 and is comparing a 36-month loan to a 60-month loan, both at 8% annual rate. The amortization schedule makes the tradeoff concrete.

36-month scenario (hypothetical): Monthly payment approximately $470. Estimated total interest approximately $1,920. By month 12, estimated remaining balance approximately $10,400. By month 24, approximately $5,500.

60-month scenario (hypothetical): Monthly payment approximately $304. Estimated total interest approximately $3,240. By month 12, estimated remaining balance approximately $12,900. By month 24, approximately $10,300.

The 60-month loan saves approximately $166 per month but costs approximately $1,320 more in total interest. The amortization schedule also shows that after 12 months of the 60-month loan, the borrower still owes approximately $12,900 - which is $2,500 more than the 36-month borrower owes at the same point, because more of each 60-month payment went to interest rather than principal.

This scenario illustrates why the remaining balance figure matters if you might sell an asset, refinance, or pay off the loan early. The 60-month borrower carries a higher balance for longer.

Scenario 2 - Extra payments at three levels: where the savings come from

A borrower has a $25,000 loan at 6.5% over 60 months. They receive a modest raise and want to understand what $100, $200, or $300 extra per month would accomplish. All numbers hypothetical.

Baseline (no extra payment): Monthly payment approximately $488. Estimated total interest approximately $4,280.

$100 extra per month: Total extra paid over term approximately $6,000 (if held for full term). Estimated total interest reduced by approximately $800-900. More practically, the balance falls faster - by month 36, the remaining balance with $100 extra is approximately $2,500 less than the baseline remaining balance.

$200 extra per month: Estimated total interest reduced by approximately $1,500-1,600. By month 36, remaining balance is roughly $5,000 less than baseline.

$300 extra per month: Estimated total interest reduced by approximately $2,000+. If $300 extra per month is enough to pay off the loan before the full 60-month term, actual total interest saved would be higher than the model shows for a full-term scenario.

The key insight: extra payments matter most early in the loan because they reduce the balance on which subsequent interest accrues across many future periods. The same $200 extra applied in month 48 of a 60-month loan saves far less interest than $200 extra applied in month 2.

Scenario 3 - Lump-sum extra payment: the tax refund scenario

A borrower has a $12,000 loan at 9% over 48 months, 10 months into the schedule. They receive approximately $1,500 in a tax refund and are deciding whether to apply it to the loan principal or use it elsewhere.

Without the lump sum: Remaining balance at month 10 is approximately $9,800. Estimated total interest remaining is approximately $1,680.

With $1,500 applied to principal at month 10: Remaining balance drops to approximately $8,300. Estimated total interest remaining falls by approximately $300-350 depending on how the lender applies the payment and when.

This is a simplified illustrative estimate. The actual savings depend on when the lender applies the payment relative to interest accrual and whether the regular payment amount stays the same (which would accelerate payoff) or adjusts (which is less common but possible with some lenders). The model assumes the regular payment continues unchanged and the lump sum reduces the balance directly.

This scenario shows a practical use of the amortization calculator: modeling whether a one-time extra payment is worth applying to the loan versus holding as savings. The answer depends on the loan interest rate compared to what the savings could earn - a comparison this calculator cannot make because it only models the loan side. That comparison requires evaluating both alternatives, which is a personal finance judgment beyond the scope of an educational calculator.

Scenario 4 - The "wrong term" risk: what happens when you can no longer make payments

A borrower takes a $18,000 auto loan at 7% over 72 months (six years) because the payment is affordable. Hypothetical monthly payment: approximately $308. Total estimated interest over 72 months: approximately $4,176.

At the end of month 24, the borrower needs to sell the vehicle due to a job relocation. The amortization schedule shows the remaining balance at that point is approximately $13,600. The vehicle has depreciated to approximately $12,000 in the used market.

The borrower owes approximately $1,600 more than the vehicle is worth. To sell the vehicle, they would need to cover that gap. If they cannot, they are in a negative equity position that constrains their options.

This scenario - often called being underwater on a loan - is more likely with long terms on depreciating assets because the amortization schedule reduces the balance slowly relative to the asset's depreciation rate. A shorter term (say 48 months at the same rate) would produce a remaining balance of approximately $10,200 at month 24 instead of $13,600 - a significant difference for a vehicle worth $12,000.

The amortization schedule makes this visible before the loan is signed. Running a 72-month schedule and a 48-month schedule side by side and checking the balance at month 24 or 36 reveals the negative equity risk before committing.

How to read your amortization schedule - a checklist

Whether you are reading the preview table in this calculator or an official schedule from a lender, work through these items to make sure you understand what the schedule is telling you.

• [ ] Find the payment amount - Confirm it matches the scheduled payment in your loan agreement or your calculator input; if they differ, identify why
• [ ] Read the first payment's interest column - This is the maximum interest charge per period; it equals the outstanding balance multiplied by the periodic rate; if the first month's interest seems wrong for the principal and rate, check the rate input and period convention
• [ ] Read the first payment's principal column - This is what you are actually reducing your debt by in month one; for long-term loans at higher rates, this can be a small fraction of the payment
• [ ] Track the remaining balance column - The balance should decrease every period; if it does not, something in the model structure is wrong
• [ ] Find the midpoint payment - At the halfway point of the term, check what percentage of the balance has been paid down; in a standard 60-month amortization, roughly 45-50% of the principal is paid off at month 30, not exactly half - because early payments cover more interest
• [ ] Check the final payment - The remaining balance should reach approximately zero; a small residual is normal rounding; a large residual may indicate a balloon payment structure or a model error
• [ ] Compare the total interest column sum to the "estimated total interest" output - They should match; any discrepancy indicates a rounding or period convention issue
• [ ] Note where the principal portion exceeds the interest portion - For most standard loans, this crossover happens past the midpoint of the term; finding this crossover period helps you understand when extra payments become less impactful
• [ ] If using an extra payment field, check the balance reduction rate - With extra payments, the balance should fall faster than the standard schedule; confirm the difference is visible in the preview table
• [ ] Compare to a lender's official schedule if you have one - Minor differences due to day-count conventions or rounding are normal; large differences in payment allocation or remaining balance may reflect fees, rate adjustments, or product-specific terms worth asking about

Limitations of this estimate

This calculator uses simplified fixed-rate amortization math. It cannot model or account for:

Your actual rate. The rate you enter is hypothetical. An actual lender's rate offer depends on your credit profile, income, existing debt, the loan type, and market conditions at origination.

Day-count conventions. Lenders use different methods for counting days between payments - actual/actual, actual/365, 30/360, and others. The method affects how much interest accrues in each period, especially in months with more or fewer days. This calculator uses simplified per-period rate math rather than a calendar-specific day count.

Late or missed payments. The model assumes every payment is made on time and in full. A missed payment would mean the balance does not decrease as scheduled, and interest would continue to accrue on a higher balance. The model does not simulate late fees, penalty rates, or modified schedules following a missed payment.

Lender-specific prepayment rules. As noted in the caution block, how a lender applies extra payments can differ significantly from this model's assumptions. Some hold payments, some require principal-only designations, and some charge prepayment penalties.

Variable or adjustable rates. This calculator models a fixed rate across the entire term. If the loan has a variable rate that can change based on an index, actual interest charges will differ from the estimate as the rate changes.

Interest-only periods. Some loan structures begin with an interest-only phase where no principal is reduced. The balance stays flat during that period - this model does not support interest-only structures.

Balloon payments. A balloon loan has a large final payment that pays off the remaining balance at the end of a shorter scheduled payment period. This calculator assumes full amortization to zero - it does not model balloon structures.

Deferred interest. Promotional financing sometimes defers interest, meaning it continues to accrue but is not charged immediately. If deferred interest is not paid off in time, it is added to the balance (capitalized). This calculator cannot model deferred interest scenarios.

The loan's official amortization table. Your lender's official amortization schedule is based on the actual contractual terms of your loan - the exact rate, the actual start date, the day-count convention, any fees, and all other product-specific rules. This calculator produces a simplified estimate for educational purposes.

Before you use this calculator - a research checklist

The amortization calculator is most useful when you already have some loan parameters to model. Before running scenarios:

• [ ] I know the principal amount I intend to borrow (or am currently repaying)
• [ ] I have a rate estimate from a pre-approval, published rate range, or existing loan agreement to use as my input
• [ ] I know the loan term in months from my intended loan or current loan agreement
• [ ] I understand that the calculator's estimates are hypothetical and will not match a lender's official schedule exactly
• [ ] I have the loan payment calculator open or available to confirm the regular payment estimate before modeling the full amortization schedule
• [ ] I have identified whether my goal is research (comparing terms before borrowing) or analysis (understanding an existing loan's cost structure)
• [ ] If I am modeling extra payments, I have confirmed with my lender or loan agreement how prepayments are actually applied

Before you sign - disclosure checklist for loans with amortization schedules

If you are evaluating a loan that comes with an amortization schedule, use this checklist before signing.

• [ ] Payment amount - The scheduled payment on the disclosure matches what you modeled; if it differs from your calculator estimate, identify the source of the difference (fees in the financed amount, a different day-count convention, rounding)
• [ ] APR vs. interest rate - Confirm both figures and understand why they differ if they do; a significant gap suggests fees are part of the financed cost - see APR glossary entry
• [ ] Finance charge - The total dollar interest and fee cost over the full term; compare it to the total interest figure in your calculator estimate; differences may reflect fees the calculator did not include
• [ ] Total of payments - All scheduled payments added together; subtract the principal to get the total interest; confirm this matches or is close to the disclosure's finance charge figure
• [ ] Amortization schedule - If the lender provides a full schedule, check the first payment's principal/interest split against what the calculator shows for similar inputs; large differences are worth asking about
• [ ] Prepayment terms - Whether early payoff or extra payments carry any fee or restriction; if there is a prepayment penalty, the extra payment scenarios from the calculator lose some or all of their benefit
• [ ] Variable rate clause - Confirm whether the rate is truly fixed for the full term or whether any provision allows it to change
• [ ] Final payment amount - Check whether the final payment matches the regular payment (standard amortization) or is significantly larger (potential balloon structure)
• [ ] Late payment terms - Grace period (if any) and late fee; missed payments disrupt the amortization schedule and can add cost beyond what the model projects

Alternatives to consider before borrowing

The amortization calculator is most often used during research. Before committing to a loan with a long amortization schedule, consider whether any of the following alternatives reduces total cost or risk.

Choose a shorter term if your budget allows. A shorter term means faster amortization, less total interest, and a lower remaining balance at any given point in the loan life. The tradeoff is a higher monthly payment. Modeling both terms in the calculator and comparing the total interest difference often reveals that the monthly payment premium for the shorter term is small relative to the interest savings.

Make a larger down payment or borrow less. A smaller principal amortizes faster and generates less total interest at the same rate and term. If you can reduce the amount you finance by saving longer before applying, the amortization schedule starts from a lower balance.

Model an extra payment before committing to it. Use the extra payment field before you decide to borrow. If a $100/month extra payment meaningfully reduces total interest on a loan you are considering, that is useful information before you sign - it may affect which term makes more sense, or whether borrowing slightly less and making extra payments is a better structure than borrowing more on a longer term.

Compare the interest cost of the loan against the opportunity cost of the funds. This calculator shows the interest cost of borrowing. It cannot compare that cost against what the same cash could do elsewhere. That comparison - whether to pay off debt faster or use extra funds differently - depends on your full financial picture and is a question for a personal finance framework beyond this calculator's scope.

Read the loans hub for the broader cost framework before modeling specific numbers. Understanding how rate, term, and fees interact at a conceptual level makes the amortization schedule easier to interpret.

Using this calculator alongside other tools on this site

Loan payment calculator - Start here to confirm the regular payment amount before using the amortization tool. The loan payment calculator uses the same inputs but focuses on the payment figure rather than the full schedule. Use it to quickly compare payment sizes across different rate and term combinations before opening the amortization view.

APR calculator - Helps you understand how fees affect the annualized cost of borrowing. If a lender's APR differs meaningfully from the rate you plan to enter in the amortization calculator, the APR tool can help you understand the fee-inclusive cost before modeling the schedule.

Personal loan calculator - Includes an origination fee input that adjusts the net financed amount, which changes what principal to enter in the amortization calculator if a fee is deducted from proceeds.

Auto loan calculator - Produces the financed amount for a vehicle purchase scenario, which you can then carry into the amortization calculator to view the full payment schedule.

Frequently asked questions

Is the preview table in this calculator a full amortization schedule?

The preview shows the first several payment periods only - not the complete schedule. A full downloadable schedule covering every payment from origination to payoff is a planned feature for a later phase of this site. For a complete schedule, your lender is the definitive source - they are required to provide one for most consumer loan products, and it governs the actual repayment terms.

Will the calculator's schedule match my lender's amortization table?

Not exactly. Even with identical principal, rate, and term, differences in day-count conventions, rounding methods, fee treatment, and other product-specific rules will produce some variation. This calculator uses simplified per-period rate math, which is accurate as a directional model but will not reproduce the precise figures in your official loan documents. Use this tool to understand the structure and model tradeoffs - use your loan agreement for the contractual schedule.

How do extra payments affect the schedule?

Extra payments applied to principal reduce the outstanding balance before the next period's interest accrues. A lower balance means less interest charges in that period - and every period that follows. The calculator models this effect when you enter an amount in the extra payment field. The schedule preview and total interest estimate both reflect the modeled extra payment. For important caveats about how lenders actually apply prepayments, see the caution block in the extra payments section above.

Does early payoff save the interest remaining on the schedule?

In a standard fixed-rate loan with no prepayment penalty, paying off the remaining balance before the scheduled end of the term means you stop paying interest from that point forward. You save the interest that would have accrued across the remaining periods. This is why the remaining balance figure in the schedule matters - it is the amount you would need to pay to exit the loan at that point. If the loan has a prepayment penalty, the savings are reduced by the penalty amount.

What does a higher rate do to the amortization pattern?

A higher rate increases the interest portion of each payment, which means less principal is paid down per period at the same fixed payment. The balance falls more slowly. If the payment and term are fixed, a higher rate means more total interest paid over the life of the loan - which the calculator reflects directly in the estimated total interest output. Running the same principal and term at different rates side by side in the calculator makes this difference visible.

If I make extra payments, will my loan end earlier than the scheduled term?

If extra payments are sufficient to pay down the balance faster than the standard schedule and the lender applies them as immediate principal reductions, the loan can reach a zero balance before the scheduled term end. This calculator models extra payments within the existing term rather than automatically computing an early payoff date. If you want to model a specific payoff date goal, experiment with the extra payment field and watch when the estimated remaining balance approaches zero in the preview table. Your actual early payoff date depends on how your lender processes the payments.

Can I use this calculator for a home-secured loan?

This calculator models standard fixed-rate amortization, which is the repayment structure used in most conventional fixed-rate home-secured loans. However, home-secured loans have additional complexity - property taxes, insurance escrow, PMI (private insurance on home loans), possible points paid at origination, and the interaction between principal balance and home equity - that this calculator does not model. For a rough understanding of principal-and-interest payment structure, the calculator may be directionally useful. For home-secured loan-specific research, resources focused on home lending provide more appropriate detail.

What happens to the amortization schedule if I miss a payment?

This calculator assumes all payments are made on time and in full. A missed payment means the balance does not decrease as scheduled, and interest continues to accrue on the higher balance. Depending on the loan agreement, a missed payment may trigger a late fee, and sustained non-payment can result in default, credit reporting, and for secured loans, collateral risk. The official schedule in your loan documents may include provisions about what happens when payments are missed. This calculator cannot simulate missed-payment scenarios.

Why does the first payment cover so little principal?

In a standard fixed-rate amortization, the interest charge in each period equals the outstanding balance multiplied by the periodic rate. At period one, the balance is at its maximum - so the interest charge is also at its maximum. Whatever is left of the fixed payment after covering that interest charge goes to principal. For high-rate or long-term loans, the interest charge can be a large fraction of the early payments. See the principal-and-interest table in the schedule reading section for a hypothetical dollar illustration of this pattern.

Is this tool relevant if I already have a loan?

Yes. If you have an existing fixed-rate loan, you can enter your current remaining balance as the principal, the original rate, and the remaining term to model the rest of your schedule. This can help you understand how much of each future payment will go to interest, what the balance will be at a specific future month, and what extra payments would save in total interest from this point forward. The starting point for this analysis is your current loan statement, which should show the outstanding principal balance.

Plainly summary

• Amortization describes how a loan balance declines through scheduled payments. In a fixed-rate loan, the payment is constant but the proportion going to interest vs. principal shifts every period - high interest share early, high principal share late.
• The total interest shown in an amortization schedule is the clearest measure of what a loan costs beyond repaying the principal. It is determined by the rate, the term, and the starting balance - not by the monthly payment alone.
• Extra payments reduce total interest by lowering the balance on which future interest accrues. The earlier in the loan life extra payments are made, the more periods benefit from the reduced balance. Always confirm with your lender how prepayments are applied before assuming these savings will match the calculator estimate.
• Longer terms mean the balance falls more slowly and more total interest accrues. Modeling a 48-month vs. 72-month schedule on the same principal makes the total interest difference concrete before you commit.
• This calculator produces simplified estimates from hypothetical inputs. Your lender's official amortization schedule - based on your actual contractual terms - is the authoritative document. Use this tool to build understanding and model tradeoffs, not as a substitute for your loan agreement.