Mortgage Calculator: Monthly Payment & Total Interest
Work out what a fixed-rate mortgage will actually cost you each month, and how much of the total goes to interest over the life of the loan.
Adjust the inputs and select Calculate for a full breakdown.
Year-by-year amortization schedule
Compare Common Scenarios
How the numbers shift across typical situations for this calculator:
| Scenario | Monthly payment | Total interest | Total of payments |
|---|---|---|---|
| $300k · 6.5% · 30-year | $1,896.20 | $382,633.47 | $682,633.47 |
| $300k · 6.5% · 15-year | $2,613.32 | $170,397.98 | $470,397.98 |
| $450k · 7.0% · 30-year | $2,993.86 | $627,790.04 | $1,077,790.04 |
| $250k · 5.5% · 20-year | $1,719.72 | $162,732.38 | $412,732.38 |
How This Calculator Works
The calculator takes your loan amount, annual interest rate, and term, then applies the fixed-rate amortization formula to find the constant monthly payment that fully repays the loan. It converts your APR to a monthly rate and the term to a number of monthly payments, then derives the payment and rebuilds the schedule month by month so you can see how principal and interest shift over time.
The Formula
Fixed-Rate Amortization
P = loan amount, r = monthly rate (APR ÷ 12), n = number of monthly payments
Worked Example
Take a $300,000 loan at 6.5% APR over 30 years. The monthly rate is 0.5417% and there are 360 payments, giving a monthly figure of about $1,896. Over the full term you repay roughly $682,600 — meaning interest alone is about $382,600, larger than the amount you originally borrowed.
Key Insight
On a 30-year mortgage, the early years are almost entirely interest. Even a small extra payment in year one removes far more lifetime interest than the same payment in year fifteen.
Frequently Asked Questions
Does this calculator include property taxes and insurance?
No. This figure is principal and interest only. Add escrow for property taxes, homeowners insurance, and any PMI separately to get your full monthly housing cost.
What interest rate should I enter?
Enter the APR your lender quoted. If you are still shopping, use the average rate for your credit tier and loan term as a planning estimate, then refine it once you have a real quote.
How does the loan term change the payment?
A longer term lowers the monthly payment but raises total interest paid, because you are borrowing the money for longer. A shorter term does the reverse.
Should I choose a 15-year or a 30-year mortgage?
A 15-year mortgage carries a higher monthly payment but cuts total interest dramatically because the balance is repaid in half the time. A 30-year keeps payments affordable but costs far more interest overall. Compare both in the scenario table above before deciding.
How much does a small rate change affect the payment?
On a large balance the effect is significant. Even a half-point difference in APR can change the monthly payment by tens of dollars and the lifetime interest by tens of thousands, which is why shopping multiple lenders is worth the effort.
Does making extra principal payments help?
Yes, substantially. Any payment above the scheduled amount goes straight to principal, which shrinks the balance that future interest is charged on and shortens the loan. The earlier in the schedule you do it, the larger the lifetime saving.
Related Calculators
Data Sources & Benchmarks
This calculator draws on 3 independent, dated sources. The starting values for loan amount and interest rate are taken from the benchmarks below and refresh whenever the snapshots are updated.
Methodology & Review
Payments use the standard fixed-rate amortization formula. Figures cover principal and interest only; escrow items such as property tax, homeowners insurance, and PMI are excluded by design. Results are reviewed against published lender amortization tables.
Written by Ugo Candido · Last updated May 17, 2026.