Methodology
How the Extra Payment & Biweekly Calculator works
How Tallivo compares a baseline mortgage against one with extra principal or biweekly payments, and computes the interest and time saved.
The formula
interest saved = interest(baseline) − interest(with extra principal)
Step by step
- The baseline loan is amortized month by month at your rate and term.
- The accelerated loan repeats the amortization, adding your extra principal to every monthly payment, until the balance reaches zero.
- Time saved = baseline payoff month − accelerated payoff month. Interest saved = the difference in total interest.
- Biweekly plans are modeled as their cash-flow equivalent: 26 half-payments a year equal 13 monthly payments — one extra full payment per year (extra = P&I ÷ 12 each month).
Assumptions & limitations
- A fixed rate and no prepayment penalty; extra amounts are applied to principal.
- Extra payments start immediately and continue every month.
- The biweekly model captures the extra-annual-payment effect, the dominant driver of biweekly savings.
Sources
Model reviewed 2025. Figures are planning estimates, not a loan offer — this is not financial advice.