Mortgage Calculator (payment & amortization)
Calculate a mortgage's monthly payment, total interest, and total cost, with a year-by-year amortization schedule showing how the balance falls.
Amortization schedule (by year)
| Year | Interest paid | Principal paid | Balance left |
|---|
How a mortgage payment is worked out
A repayment mortgage uses a level payment: the same amount every month for the whole term, calculated so the balance reaches exactly zero on the final payment. The formula behind it is the standard annuity payment.
M = P · i / (1 − (1 + i)⁻ⁿ)
P is the amount borrowed, i the monthly interest rate (annual rate ÷ 12), and n the number of monthly payments. Because interest compounds monthly, you can't just divide the annual rate across the term.
Why early payments are nearly all interest
Each month's interest is charged on the balance still outstanding, so at the start — when you owe the most — interest eats most of the payment and very little goes to the debt. As the balance falls, the interest portion shrinks and the principal portion grows, accelerating toward the end. The schedule above shows this crossover year by year, and it's why overpaying early saves far more than overpaying late.
Worked example
Borrowing 200 000 over 30 years at 6% gives a monthly payment of about 1199. Over 360 payments that's roughly 431 700 in total — more than 231 000 of it interest, so you repay well over double what you borrowed. Cutting the term to 15 years raises the payment to about 1688 but slashes total interest to around 103 800.
What this doesn't include
This is the loan repayment only. Real mortgage costs also include property tax, buildings insurance, any mortgage insurance, and fees — and most rates are fixed only for an initial period before reverting. Treat the figure as the core repayment, not the full monthly cost of owning.