How it works
Extra payments go straight to principal, so every later month charges interest on a smaller balance. Ask your servicer to apply extra money to principal, and check there is no prepayment penalty.
FAQ
How much does $200 extra a month save on a $320,000 mortgage at 6.5%?
About $105,000 of interest, and you finish about 6½ years sooner.
Sources (checked Nov 6, 2026): Standard amortization.