Mortgage Extra Payments Calculator with Bi-Weekly Payments

Calculations use discrete periodic amortization formulas: periodic rate = APR / periods_per_year; scheduled payment solves the standard annuity equation and the number of remaining periods with extra recurring payment is solved algebraically when payment exceeds the interest portion. For true bi‑weekly we use 26 periods per year; for the shortcut we split the monthly scheduled payment in half and treat that as the bi‑weekly scheduled amount.

The tool is intended for estimation and education. It applies a one‑time reduction immediately (t=0) for simplicity. Lender processing, interest compounding conventions, escrow, prepayment penalties, daily interest accrual, and rounding rules can alter real‑world results. See accuracy and compliance notes below.

Choose the payment frequency scenario to compare how recurring extras or a one‑time principal payment reduce interest and shorten the loan.

Numbers are estimates based on standard amortization formulas. Verify final payoff figures with your lender.

Example: $300,000 at 3.5% for 30 years. The true bi‑weekly schedule (26/year) with zero extras shortens the schedule slightly versus monthly; adding a $100 extra to each bi‑weekly payment reduces payoff time and saves interest. Use the form to view numeric outputs.

If you instead split the monthly payment in half and pay that bi‑weekly (monthly/2 shortcut), you effectively make one extra monthly payment per year (13 months of payment), which accelerates payoff compared with strict monthly payments but is not identical to lender bi‑weekly processing.