Paying half your payment every two weeks adds up to one extra payment a year — shortening your loan and cutting interest automatically.
There are 52 weeks in a year, so paying half your monthly amount every two weeks means 26 half-payments — the equivalent of 13 monthly payments instead of 12. That one extra payment each year goes to principal and quietly shortens your loan.
True bi-weekly billing requires a servicer that applies payments every two weeks. You can get the same result yourself by adding one-twelfth of your payment to principal each month — which is exactly what this calculator models.