15-Year Home Loan Refinance Payment Calculator

This 15-year home loan refinance calculator estimates the monthly principal-and-interest payment and total interest on a new fixed-rate loan. Enter the amount you would refinance and the annual APR you receive from a lender; the results are estimates, not a rate quote or approval decision.

Formula

The calculator uses the standard fixed-payment amortization formula. Monthly payment = loan principal × monthly rate ÷ [1 − (1 + monthly rate)^{−number of payments}]. It rounds the payment to the nearest cent before calculating total interest.

• amt is the refinanced loan principal, in dollars.
• apr is the annual percentage rate entered as a percentage, such as 6.5 for 6.5% per year.
• r, the monthly rate in decimal form, equals apr ÷ 1,200.
• n, the number of monthly payments, is 15 × 12 = 180.
• pmt is the rounded monthly principal-and-interest payment, in dollars.
• int is pmt × 180 − amt, in dollars.

The payment formula assumes equal monthly payments and a constant rate. The total-interest result uses the rounded payment, as a real payment schedule is normally expressed in cents. The APR field is an input, not a current market-rate estimate; use the figure in a lender’s quote or disclosure when comparing scenarios.

Worked Example

Using the defaults shown above: a $300,000 principal, a 6.5% APR, and 180 monthly payments.

1. Convert the APR to a monthly decimal rate: 6.5 ÷ 1,200 = 0.0054166667.
2. Substitute the values: payment = 300,000 × 0.0054166667 ÷ [1 − (1 + 0.0054166667)⁻¹⁸⁰].
3. The unrounded result is about $2,613.28; rounded to cents, the monthly principal-and-interest payment is $2,613.28.
4. Total of the rounded payments: $2,613.28 × 180 = $470,390.40.
5. Total interest estimate: $470,390.40 − $300,000 = $170,390.40.

Assumptions

• The interest rate remains fixed for all 15 years.
• Payments are made monthly, at the end of each monthly period, with the first payment one month after the loan begins.
• Interest compounds monthly using APR ÷ 12.
• The estimate excludes closing costs, lender fees, taxes, homeowners insurance, mortgage insurance, escrow, and any other charges. It also does not model changes in the balance from extra payments or missed payments.

When to Use This Calculator

Use it to see the payment and scheduled interest for a proposed 15-year refinance under a particular principal and APR. The principal might be the amount needed to pay off an existing mortgage, but a refinance quote can include financed costs or other adjustments. Enter the actual proposed loan amount rather than assuming it equals your current balance.

You can also run separate scenarios by changing the principal or APR to match figures supplied by a lender. This is a mathematical comparison, not a prediction of what a lender will offer. Ask the lender for the rate, APR, loan amount, payment schedule, and itemized costs applicable to your situation.

How to Read the Results

The first result is the estimated monthly principal-and-interest payment. It is not necessarily the full amount due each month: property taxes, homeowners insurance, mortgage insurance, and escrow deposits may be billed separately or collected with the payment. The second result is the estimated interest across 180 payments, not the total amount paid; adding the principal gives the scheduled payment total before excluded costs.

A shorter term has fewer scheduled payments than a longer term, but that fact alone does not tell you whether refinancing fits your circumstances. Compare complete loan disclosures, including the amount financed, APR, fees, and payment details. This calculator does not estimate how long it takes to recover refinance costs or account for the remaining term and interest on an existing mortgage.

Common Mistakes and Limits

Enter the APR as a percentage number: type 6.5 for 6.5%, not 0.065 or 6.5% as a decimal. Enter a dollar principal without typing a currency symbol. A small APR-entry error can materially change the estimated payment.

Do not treat the payment as a complete housing budget. The formula covers principal and interest only, and it does not incorporate lender fees into the loan unless you include them in the principal yourself. Doing so changes the amount being modeled; it still does not show which charges are financed or paid upfront.

The formula also assumes payments are made on schedule and the rate does not change. Actual lender calculations may differ because of payment dates, rounding practices, fees, or loan terms that are not represented here. The result is an estimate; the lender’s disclosure gives the exact figures.

Frequently Asked Questions

What does a 15-year refinance payment include?
The calculator’s payment includes estimated principal and interest only. It does not include taxes, insurance, mortgage insurance, escrow, or fees.

How do I find the APR to enter?
Use the APR listed in the specific loan quote or disclosure you are evaluating. Do not substitute a general advertised rate or assume the calculator predicts an offer.

Is the refinance amount the same as my current mortgage balance?
Not necessarily. The new principal depends on the proposed loan and any costs or other amounts included in it. Use the amount supplied for the refinance scenario.

Why can the monthly payment be higher on a 15-year term?
The same principal is repaid over fewer monthly payments than on a longer term. The calculator uses 180 payments, so it does not represent a longer repayment schedule.

Does this result show whether refinancing saves money?
No. It estimates payments and interest on the new loan only. It does not compare that schedule with the remaining payments, costs, or timing of an existing mortgage.

Final Thoughts

A 15-year refinance estimate depends on the principal and APR entered, while the calculator keeps the term fixed at 180 monthly payments. Use figures from a lender’s actual quote and review its full disclosure for costs and payment details; this arithmetic is educational and is not financial advice.

Related

• Reducing Balance Loan Formula and Calculator
• Principal Balance on a Loan: How It Works
• Reducing Balance Loan Calculator and Formula

in amt | Refinance loan amount | $ | 300000 | 1 | 100000000
in apr | Interest rate (APR) | % | 6.5 | 0.01 | 100
out pmt | Monthly principal-and-interest payment | $ | round(amt * (apr / 1200) / (1 - (1 + apr / 1200) ^ -180), 2) | 2
out int | Total interest over 15 years | $ | pmt * 180 - amt | 2