Bi-Weekly vs Monthly Payment

How Bi-Weekly vs Monthly Payment works

This tool models two repayment schedules for the same car loan. The monthly schedule applies one payment per month over the term. The bi-weekly schedule splits that monthly payment in half and applies it every two weeks—resulting in 26 payments per year, or the equivalent of 13 monthly payments annually. Because interest accrues on the outstanding balance, the extra payment each year reduces principal faster, cutting both total interest and payoff time.

The formula

The calculator first computes the standard monthly payment M using the closed-form amortisation formula: M = P · r · (1 + r)ⁿ / [(1 + r)ⁿ − 1], where P is principal, r is the periodic interest rate (APR ÷ 12 ÷ 100), and n is the term in months. Total monthly-schedule interest is M · n − P. For the bi-weekly schedule, it runs a period-by-period simulation: each fortnight it subtracts M / 2 from the balance, applies interest at rate APR / 26 / 100, and iterates until the balance reaches zero. The difference between the two total-interest figures is the saving.

Where this method is most accurate

Amortisation simulation is exact for fixed-rate loans with no fees, prepayment penalties, or payment holidays. It assumes that bi-weekly payments align with the lender's interest-accrual calendar; some lenders hold bi-weekly payments in escrow and remit monthly, which negates the benefit. The calculation also excludes arrangement fees, early-settlement charges, and any variable-rate clauses that may adjust APR mid-term.

What this tool does not do

It does not model balloon payments, interest-only periods, or deferred-payment schemes. It does not account for taxes, registration fees, insurance premiums, or currency-conversion costs. The output reflects the mathematical structure of the two schedules but does not constitute a contract comparison or a recommendation to switch payment frequency. Lenders may impose administrative rules or fees that alter the real-world saving.

Disclaimer

This calculator is an educational tool that performs pure arithmetic on user-supplied inputs. It does not provide financial advice, recommend any lender or payment plan, or guarantee any particular saving. Actual loan terms, fees, and eligibility criteria vary by institution and jurisdiction. Users bear sole responsibility for verifying calculations and consulting a qualified financial professional before making borrowing or repayment decisions.