Loan and mortgage calculator

Payment and schedule — amount, annual rate, term, and payment frequency give the level payment P·r / (1 − (1+r)^−n), where r is the annual rate divided by payments per year and n the number of payments. Interest is worked out on the balance each period and rounded to the cent, as lenders do, so totals match a real statement to within a few cents. The chart stacks principal and interest by year with the balance as a line; the schedule shows each year or every payment and downloads as CSV.

Extra payments — a recurring amount added to each payment (from a chosen payment onward) and any number of lump sums. The tool compares against the plain schedule: how many payments sooner the loan ends and how much interest that saves. Extra money goes straight to principal.

Payment frequency — bi-weekly re-amortises over 26 payments a year (about the same total as monthly); accelerated bi-weekly pays half the monthly payment every two weeks, which is one extra monthly payment a year and takes several years off a 30-year mortgage.

Refinance — monthly payment now and after, the monthly saving, the break-even point (closing costs ÷ monthly saving), and the total remaining cost of each loan. A longer new term can lower the payment and still cost more overall, so compare totals.

Affordability — the largest loan whose housing cost (principal and interest, property tax, insurance, HOA, and mortgage insurance when less than 20% is down) fits both the front-end ratio (housing ÷ gross monthly income) and the back-end ratio (housing plus other debts ÷ income). 28/36 is a common guideline; real lenders and programmes vary.

APR with fees — the rate at which the monthly payments exactly repay the amount you actually receive (loan minus prepaid finance charges). Useful for comparing offers with different fees and points; which fees count is defined by law in each country.