30-Year Loan APR: Estimate Payments and Total Interest

This calculator estimates the monthly principal-and-interest payment and total interest for a fixed-rate loan repaid over 30 years. Enter the loan amount and annual APR to see the payment schedule’s basic cost; use the lender’s disclosed APR and loan terms for a more accurate estimate.

Formula

The calculator uses the standard level-payment amortization formula. First, it converts the annual APR to a monthly rate and converts the term in years to a number of monthly payments.

Monthly payment: M = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]. Total interest: I = M × n − P.

• P is the starting loan principal in dollars.
• APR is the annual percentage rate entered as a percentage, such as 6.5.
• r is the monthly rate, APR ÷ 1,200.
• n is the number of monthly payments, years × 12.
• M is the monthly principal-and-interest payment in dollars, rounded to cents.
• I is total interest in dollars, calculated using the rounded monthly payment.

A 30-year term means 360 monthly payments. APR is an annualized rate; this estimate applies a monthly rate of APR divided by 12, as specified in the calculator assumptions. It does not attempt to reconstruct every fee or APR calculation a lender may use.

Worked Example

Using the calculator’s defaults: principal P = $300,000, APR = 6.5%, and term = 30 years.

1. Convert the APR to a monthly rate: r = 6.5 ÷ 1,200 = 0.0054166667.
2. Convert the term to payments: n = 30 × 12 = 360.
3. Substitute into the payment formula: M = round[300,000 × 0.0054166667 ÷ (1 − (1.0054166667)⁻³⁶⁰), 2] = $1,896.20 per month.
4. Calculate total interest using the rounded payment: I = $1,896.20 × 360 − $300,000 = $382,632.00.

Assumptions

• The interest rate remains fixed for the full term.
• Payments are made monthly, at the end of each period, with the first payment one month after borrowing.
• Interest compounds monthly at APR ÷ 12.
• The estimate excludes lender fees, taxes, insurance, mortgage insurance, escrow, and any separate costs not entered as calculator inputs.

Using a 30-Year Loan APR Estimate

Enter the amount borrowed, not the property price or purchase budget. If a down payment or other funds reduce the amount financed, use the resulting principal. Enter the annual APR as a percentage: type 6.5 for 6.5%, not 0.065. The calculator accepts APR values from 0.01% through 100% and terms up to 50 years; the default term is 30 years.

The first result is the estimated monthly principal-and-interest payment. It is not necessarily the full monthly housing payment or a lender’s final amount due. A housing payment may also include taxes, insurance, mortgage insurance, association charges, or escrowed costs, none of which this calculator estimates.

The second result is total interest over the stated term, based on the payment rounded to cents. It assumes every scheduled payment is made as calculated and that the loan is not paid off early, modified, or affected by a changing rate. For a different term, enter the applicable number of years; keeping the APR and principal unchanged while changing the term recalculates both outputs.

Common Mistakes and Limits

Do not confuse APR with a monthly rate. The input is an annual percentage, and the formula divides it by 1,200 to obtain a monthly decimal rate. For example, 6.5% becomes 0.0054167 per month—not 6.5 or 0.065 per month.

Also avoid treating the result as a complete quote. The formula models one fixed-rate balance with equal monthly payments. Actual disclosures can reflect fees, payment dates, rounding methods, and other contract details; the calculator has no fields for these. If the loan has a variable rate, interest-only period, balloon payment, irregular payments, or added charges, this simple formula will not represent those features.

Small differences can appear because the payment is rounded to the nearest cent and then multiplied by 360 to estimate total interest. A lender’s final payment schedule may handle rounding or the final installment differently. Use the APR and principal shown in the lender’s disclosure when comparing the arithmetic with a specific loan offer, and check whether any costs are included in the APR figure.

This calculator provides estimate arithmetic for education, not financial advice. It does not assess approval, affordability, or whether a loan is suitable. The result is an estimate, and the lender’s disclosure gives the exact figures.

How to Use This List

Start with the principal and APR shown in the loan documents or quote, then set the term to 30 years if that is the schedule you want to model. Review the monthly payment and total interest together: the payment describes the scheduled monthly principal-and-interest amount, while total interest accumulates across the full modeled term. For a fuller picture, separately identify costs the calculator excludes and consult the lender’s itemized disclosure rather than adding unsupported estimates here.

Frequently Asked Questions

What does APR mean here?
It is the annual percentage rate entered as a percentage; the formula converts it to a monthly rate by dividing by 1,200.

Does the monthly result include property taxes and insurance?
No. It estimates principal and interest only, excluding taxes, insurance, mortgage insurance, escrow, and fees.

Why can the total interest differ from a lender’s figure?
The calculator assumes a fixed rate, equal monthly payments, and cent-rounded payments; lender calculations may include charges or use contract-specific timing and rounding.

Can I use a different loan term?
Yes. Enter the term in years; the calculator converts it to monthly payments, with a maximum input of 50 years.

Does this show how much a lender will approve?
No. It is a payment and interest estimate only and does not model underwriting or approval criteria.

Final Thoughts

A 30-year APR estimate turns a principal, annual rate, and repayment term into a consistent monthly-payment and total-interest calculation. Treat the outputs as a starting point for understanding the arithmetic, and rely on the lender’s disclosure for the exact loan figures.

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in p | Loan amount | $ | 300000 | 1 | 100000000
in apr | Interest rate (APR) | % | 6.5 | 0.01 | 100
in yrs | Loan term | years | 30 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2