Mortgage Prepayment Calculator

See how many months an extra monthly payment or a one-off lump sum takes off your home loan, and how much interest it saves, while keeping the same instalment and a fixed rate.

Current instalment = principal × i ÷ (1 − (1 + i)^−n), with i = annual rate ÷ 12 and n = remaining months. Each month, interest = remaining principal × i and anything paid above that reduces principal. With prepayment, the lump sum comes off today and the instalment plus extra is paid every month until the principal is gone; months and interest are compared with no prepayment.

Hand check: THB 1,200,000 at 0% over 10 years is THB 10,000 a month. Adding THB 2,000 pays THB 12,000 and clears it in 100 months, 20 months sooner. THB 100,000 at 12% over 1 year has an instalment of THB 8,884.88 and THB 6,618.55 total interest; paying it all today saves that whole amount.

Uses one fixed rate and equal monthly interest; real banks accrue daily and rates may change by contract period. Some contracts have early-redemption fees or rules for applying extra payments, so confirm with your bank first and keep an emergency fund.