15-Year Loan Payment Calculator and Comparison

This 15-year loan calculator estimates the monthly payment and total interest for a fixed-rate loan, then lets you compare those figures with another term or rate by changing the inputs. Enter the loan amount, annual APR and term in years to see the estimated payment and interest.

Formula

The calculator uses the standard fixed-payment amortization formula. First it converts the annual percentage rate (APR) to a monthly rate and the term in years to a number of monthly payments:

r = APR / 1,200
n = years × 12
Monthly payment = P × r / [1 − (1 + r)⁻ⁿ]

Total interest = (monthly payment × n) − P

• P is the amount borrowed, in dollars.
• APR is the annual interest rate entered as a percentage, such as 8 for 8%.
• r is the monthly interest rate as a decimal.
• n is the total number of monthly payments.

The payment is rounded to the nearest cent before total interest is calculated. This makes the displayed total consistent with multiplying the displayed monthly payment by the number of payments. Real loan statements may differ slightly because of payment dates, lender rounding, fees or other contract details.

Worked Example

Using the calculator’s defaults: a $20,000 loan, 8% APR and a five-year term.

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to monthly payments: 5 × 12 = 60.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 per month, rounded to cents.
4. Calculate total interest using the rounded payment: ($405.53 × 60) − $20,000 = $4,331.80.

These are estimates under the assumptions below. The first payment may be due on a date that changes the lender’s exact interest calculation.

Assumptions

• The interest rate is fixed for the full term.
• There are equal monthly payments, made at the end of each monthly period.
• Interest compounds monthly at APR divided by 12.
• The calculation excludes fees, taxes, insurance, PMI and escrow costs.

How to Compare a 15-Year Loan

A 15-year term means 180 monthly payments. To model it, enter 15 in the term field and use the quoted amount and APR supplied for the loan you are evaluating. For a useful comparison, keep the loan amount the same when comparing terms; otherwise, payment differences may come from borrowing different amounts rather than the repayment schedule.

Compare at least the monthly payment and total interest, but remember they answer different questions. A shorter term generally means fewer scheduled payments and, at the same positive APR and principal, less total interest. Its monthly payment is usually higher because the principal is repaid over fewer months. A longer term spreads repayment out, which can lower the scheduled monthly payment while increasing total interest under otherwise identical assumptions.

For instance, compare two calculator runs using the same principal and APR, changing only the term to 15 years and then to 30 years. The calculator reports the scheduled payment and total interest for each scenario. This is a mathematical comparison, not a prediction of what a lender will offer: actual rates, fees and eligibility terms must come from the lender’s own figures and disclosures.

What the Calculator Includes—and Leaves Out

The calculator models principal and interest for a fully amortizing, fixed-rate loan. In a fully amortizing schedule, each payment covers that period’s interest and reduces some principal, with the balance scheduled to reach zero after the final payment. Early payments typically include a larger interest share than later payments because interest is calculated on the outstanding balance.

The result is not necessarily the amount due each month on a mortgage or other secured loan. Property taxes, homeowners insurance, mortgage insurance, escrow deposits and association charges are not included. Upfront charges and recurring fees are not included either. If those costs apply, use the figures provided by the lender or relevant service provider for a broader cash-flow estimate.

APR is an input, not a quote or a forecast. The default 8% is only an example for demonstrating the arithmetic. Enter the rate and loan amount from the specific offer or disclosure you are comparing. If an offer includes fees or a variable rate, this simple fixed-rate model will not fully represent its cost or future payment changes.

Common Comparison Mistakes and Limits

• Comparing different principals: Use the same amount borrowed to isolate the effect of a term or rate.
• Treating payment as total cost: A smaller monthly payment does not by itself mean less interest over the life of a loan.
• Confusing APR with a monthly rate: Enter an annual percentage such as 6.5, not 0.065 or the monthly rate. The calculator divides APR by 1,200.
• Ignoring costs outside principal and interest: Fees, insurance, taxes and escrow can affect out-of-pocket costs but are not calculated here.
• Assuming an exact payoff schedule: Extra payments, late payments, payment-date conventions and rate changes can alter actual balances and interest.

The formula also assumes the payment is made as scheduled and that the full loan amount is advanced at the start. It does not calculate a variable-rate schedule, balloon payment, interest-only period, refinancing costs or the effect of additional principal payments. To compare a 15-year option with another offer, use each offer’s disclosed principal, APR and term consistently, and separately account for costs the calculator omits.

Frequently Asked Questions

How many payments are in a 15-year loan?
A standard monthly-payment schedule over 15 years has 180 payments: 15 × 12. The actual schedule can vary if the contract uses a different payment frequency or timing.

Does a 15-year loan always have a lower total interest cost?
Not in every comparison. With the same principal and positive fixed APR, a shorter term normally produces less total interest than a longer term because the balance is repaid sooner. Different rates, fees or loan amounts can change the comparison.

Why is the payment higher on a shorter term?
The same principal has to be repaid in fewer installments. At the same rate and amount, that generally raises each scheduled payment, even though fewer payments can reduce total interest.

Does this calculator include taxes, insurance or fees?
No. It estimates principal-and-interest payments and interest only. Use the applicable lender disclosures and cost figures to assess expenses not represented here.

Can I use this to compare a variable-rate loan?
Only as a limited snapshot using one assumed APR. A variable rate can change over time, so its future payments and total interest cannot be represented by this fixed-rate calculation.

This result is an estimate for education; the lender’s disclosure gives the exact figures.

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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2