Loan

How it works: the payment comes from the standard amortization formula, and every row after that is worked out one month at a time — interest on what is left, the rest off the balance. The part worth staring at is the early years, where almost everything you send goes to interest and the balance barely moves. That is also why a small extra payment matters so much: it comes off the balance directly, so it never accrues interest again for the whole remaining term. On a thirty-year mortgage at six and a half percent, two hundred dollars a month saves over a hundred thousand dollars and finishes nearly seven years early. Nothing here is stored or sent anywhere, and there is nobody to hand your number to.