30-Year Refinance Monthly Payment Calculator

This calculator estimates the monthly principal-and-interest payment for a refinanced loan repaid over 30 years. Enter the new loan amount and its quoted APR to see the estimated payment and total interest; compare those figures with the lender’s loan estimate for fees and other costs.

Formula

The fixed monthly payment is calculated as M = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]. Here, M is monthly principal and interest in dollars, P is the new loan amount in dollars, r is the monthly interest rate as a decimal (APR ÷ 1,200), and n is the number of monthly payments (term in years × 12). The second result is estimated total interest: I = M × n − P, in dollars; it uses the displayed, cent-rounded payment.

Worked Example

Using the calculator’s defaults: loan amount P = $200,000, APR = 6.5%, and term = 30 years.

• Monthly rate: r = 6.5 ÷ 1,200 = 0.0054166667.
• Number of payments: n = 30 × 12 = 360.
• Payment before cent rounding: $200,000 × 0.0054166667 ÷ [1 − (1.0054166667)⁻³⁶⁰] ≈ $1,264.14.
• Estimated total interest: $1,264.14 × 360 − $200,000 = $255,090.40.

The estimated monthly principal-and-interest payment is $1,264.14. Small differences can occur if an actual loan uses a different payment schedule or rounding convention.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal monthly payments made at the end of each period.
• Interest compounds monthly at APR ÷ 12.
• The estimate excludes closing costs, lender fees, taxes, homeowners insurance, mortgage insurance, and escrow. Those costs are not included in the principal unless you add them to the loan amount yourself.

How to Use This Calculator

Enter the expected new principal, the APR quoted for that loan, and the term in years. For a 30-year refinance, leave the term at 30. The principal is generally the amount being financed, which may differ from the current payoff balance if costs are paid separately or included in the new balance. Use figures from a lender’s written quote rather than assuming a rate or fee.

The first result is the estimated monthly amount for principal and interest only. The second is the sum of those rounded monthly payments minus the starting principal. It is a mathematical estimate over the full term, not a payoff quote. The calculation assumes every scheduled payment is made and the loan is not paid off early, modified, or otherwise changed.

To make a like-for-like comparison, use the same proposed loan amount and term across estimates, then account separately for upfront costs and any costs rolled into the balance. A longer term spreads repayment over more months; that changes both the monthly payment and the total interest calculation. The calculator does not determine whether refinancing is suitable for a particular household or predict an approval decision.

Common Mistakes and Limits

Do not enter a percent as a decimal: for example, enter 6.5 for 6.5% APR, not 0.065. The formula converts the annual percentage rate to a monthly decimal by dividing by 1,200. Enter the loan term in years, not months; the calculator converts years to monthly payments. Use the new loan amount, not the old monthly payment or the home’s value.

APR and note rate may not be identical in a lender’s documents, and the calculator treats the entered APR as the fixed rate used in the payment formula. APR can reflect certain borrowing costs, but this calculator does not itemize fees or independently reproduce a lender’s APR calculation. Ask the lender which rate figure to use when comparing a quoted payment.

Rounding each payment to cents means multiplying the displayed payment by 360 may differ slightly from a lender’s final payment schedule, especially for the last installment. The estimate also excludes escrow and other charges that can affect the amount paid each month. It does not calculate break-even time, home equity, tax outcomes, or whether a borrower qualifies; those require information and rules outside this formula.

This result is an estimate, and the lender’s disclosure gives the exact figures.

Frequently Asked Questions

Does the payment include property taxes or homeowners insurance?
No. It estimates principal and interest only; taxes, insurance, mortgage insurance, and escrow are excluded.

What loan amount should I enter?
Enter the proposed new principal financed, based on a lender’s quote or your own clearly defined estimate. Costs added to the balance increase that amount.

Why does total interest appear high over 30 years?
The result adds the interest portion implied by every scheduled payment across 360 months, assuming the loan stays in place for the entire term.

Can I use this for an adjustable-rate loan?
It can show a simplified payment only if the entered rate is treated as fixed; it does not model future rate adjustments.

Does this tell me whether refinancing will save money?
No. It calculates a payment and term-wide interest estimate, but does not compare closing costs, the existing loan, or the time you expect to keep the new loan.

Final Thoughts

Use the estimate to understand how principal, APR, and a 30-year term shape a monthly principal-and-interest payment. For a full picture, verify the quoted loan amount, payment, costs, and assumptions against the lender’s disclosure.

Related

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in p | New loan amount | $ | 200000 | 1 | 100000000
in apr | Interest rate (APR) | % | 6.5 | 0.01 | 100
in yrs | Loan term | years | 30 | 0.0833 | 50
out pmt | Monthly principal and interest payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest over term | $ | pmt * yrs * 12 - p | 2