Mortgage Interest Calculator with Bi-Weekly Payments

The calculator uses the standard amortizing loan formula applied to the chosen payment frequency. It computes the periodic interest rate by dividing the annual nominal rate by the number of payments per year, then applies the fixed-payment annuity formula to determine the required payment that amortizes the principal over the specified term.

Extra payments are treated as a constant additional amount applied each period. This implementation assumes payments are applied at the same regular cadence and that the lender accepts and applies extra payments directly to principal at each period.

Results are numeric estimates for planning and comparison. They do not substitute for an official amortization schedule provided by your lender. Differences can arise from lender-specific application of extra payments, rounding rules, payment timing, escrow, fees, and day-count conventions.

This calculator gives planning estimates for periodic payment amounts, total paid, and total interest for monthly, bi-weekly, or weekly cadences. It uses the standard annuity formula adjusted for the chosen frequency and allows for a constant extra payment per period.

For legally binding numbers, exact payoff dates, or lender-specific application of extra payments, obtain an official amortization schedule from the lender or loan servicer.

Example: $300,000 principal, 4.5% annual rate, 30 years, bi-weekly (26). The calculator returns the required bi-weekly payment, total number of payments = 780, total paid and total interest for the 30-year schedule assuming no lender-enforced rounding or differing payment application rules.

If you add a modest extra amount per bi-weekly payment, the calculator reflects higher periodic payments and shows the resulting reduction in total paid and total interest for the original nominal term; exact payoff date reduction is approximate here and may require a full amortization table to determine precise payoff timing.