Mortgage Calculator

Each month, interest is calculated on the balance you still owe: balance × (annual rate ÷ 12). Whatever remains of your payment goes to principal. Because the balance falls a little each month, the interest portion shrinks and the principal portion grows — every month, for the life of the loan.

That is why early payments are so interest-heavy. On a 30-year loan at 6.5%, roughly three-quarters of the first payment is interest. It takes about eighteen years before principal and interest are even.

The interest-heavy start is not a lender trick — it falls directly out of charging interest on the outstanding balance. But it has two consequences worth acting on:

• Refinancing resets you to the start of the curve. Eight years into a 30-year loan you have finally reached the part where meaningful principal is being retired. A fresh 30-year term puts you back at the interest-heavy beginning, which is how a lower rate can still produce more total interest. The refinance calculator shows the break-even that decides it.
• Early extra payments are disproportionately powerful. A dollar of principal removed in year two eliminates far more future interest than the same dollar in year twenty. See the extra payment calculator.

Download CSV generates the file locally — no server sees your figures. The file includes a UTF-8 byte-order mark so Excel reads currency symbols correctly, uses CRLF line endings, and writes numbers unformatted so spreadsheets parse them as values rather than text. It opens directly in Excel, Google Sheets and Numbers, and carries the escrow columns and the total alongside principal and interest.

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