Mortgage Calculator
Estimate your monthly payment and see the full amortization schedule, total interest, and how extra payments shorten your loan.
How this mortgage calculator works
Enter your loan amount, interest rate (APR) and term. The calculator returns your fixed monthly principal-and-interest payment, the total interest you’ll pay over the life of the loan, and a month-by-month amortization schedule you can download as CSV.
Early in a fixed-rate mortgage, most of each payment is interest because interest is charged on a large remaining balance. As the balance falls, more of every payment goes to principal — which is why the “Loan balance over time” chart curves downward faster near the end.
A worked example
Take a $300,000 loan at 6.5% over 30 years. The monthly principal-and-interest payment works out to $1,896.20. Over the full term you’d pay about $682,633 in total — which means roughly $382,633 in interest, more than the amount you originally borrowed. That gap between what you borrow and what you repay is the single most useful number this calculator surfaces.
How the loan term changes the cost
A shorter term means a higher monthly payment but far less total interest, because you’re borrowing the money for fewer years. Here’s the same $300,000 loan at 6.5% across three common terms:
| Term | Monthly payment | Total interest |
|---|---|---|
| 15 years | $2,613.32 | $170,398 |
| 20 years | $2,236.72 | $236,813 |
| 30 years | $1,896.20 | $382,633 |
Moving from 30 to 15 years more than doubles the speed of payoff and saves over $212,000 in interest — but the monthly payment rises by about $717. The right term is the shortest one whose payment still fits comfortably in your budget.
What extra payments do
Adding even a small extra monthly payment goes entirely toward principal, which removes all the future interest that principal would have generated. On the 30-year loan above, paying just $200 extra each month pays the mortgage off in about 23 years instead of 30 and saves roughly $103,000 in interest. Type an amount into “Extra monthly payment” in the calculator to see the effect on your own numbers.
What’s included — and what isn’t
This tool shows principal and interest only. Your real monthly housing cost also includes property tax, homeowners insurance, and (if your down payment is under 20%) private mortgage insurance (PMI). Those vary by location and lender, so estimate them separately and add them to the payment shown above.
Frequently asked questions
How is a monthly mortgage payment calculated?
It uses the amortization formula M = P·r / (1 − (1 + r)−n), where P is the loan amount, r is the monthly rate (annual APR ÷ 12), and n is the total number of monthly payments. Interest each month is charged on the remaining balance; the rest of the payment reduces principal.
How much can extra payments save me?
Every extra dollar goes straight to principal, so it shortens the loan and removes all the future interest that principal would have generated. Type an amount into “Extra monthly payment” to see your new payoff time and the interest saved.
Does this include taxes and insurance?
No — it’s principal and interest only. Add property tax, homeowners insurance and any PMI on top for your full monthly cost.
Should I choose a 15-year or 30-year mortgage?
A 15-year loan has a higher monthly payment but dramatically less total interest, while a 30-year loan keeps the monthly cost low and frees up cash flow. As a rule of thumb, pick the shortest term whose payment you can comfortably afford. If you like the flexibility of the lower 30-year payment, you can still pay extra in good months to get much of the 15-year savings without being locked into the higher payment.
What’s the difference between the interest rate and the APR?
The interest rate is what’s used to calculate your monthly principal-and-interest payment. The APR (annual percentage rate) is a broader figure that also folds in certain lender fees and points, so it’s usually slightly higher than the rate. This calculator uses the rate you enter to compute the payment; compare lenders on APR to judge the true cost.
How much of a down payment do I need?
Many conventional loans allow as little as 3–5% down, but putting down less than 20% usually means paying private mortgage insurance (PMI) until you build enough equity. A larger down payment lowers your loan amount, your monthly payment and your total interest. Enter your expected loan amount (home price minus down payment) above to see the difference.
Last updated: July 2026 · How we calculate
BriskToolbox provides estimates for general information only and is not financial advice. Confirm exact figures with your lender.