Cernarus

Mortgage Extra Payments Calculator with Bi-Weekly Payments

This calculator compares standard monthly amortization and two common bi‑weekly approaches (a true 26‑payment schedule and the monthly/2 shortcut) to show how recurring extra payments or an immediate one‑time principal reduction affect payoff time and total interest.

Results assume the extra payment is applied to principal at each scheduled payment. A one‑time reduction field models an immediate principal payment at time zero. Use the payment frequency selector to compare scenarios side‑by‑side.

Updated Nov 5, 2025

Exact bi‑weekly schedule using 26 equal payments per year and the corresponding periodic rate. Recurring extra is applied each bi‑weekly payment. One‑time immediate reduction is supported.

Inputs

Results

Updates as you type

Scheduled bi‑weekly payment

$621.48

Payment with extra (bi‑weekly)

$621.48

Estimated payoff (years)

—

Total interest with extra

—

Interest saved

—

Payments saved (bi‑weekly)

—

OutputValueUnit
Scheduled bi‑weekly payment$621.48USD
Payment with extra (bi‑weekly)$621.48USD
Estimated payoff (years)——
Total interest with extra—USD
Interest saved—USD
Payments saved (bi‑weekly)——
Primary result$621.48

Visualization

Methodology

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.

Worked examples

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.

Key takeaways

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.

Further resources

Expert Q&A

Does making bi‑weekly payments always save interest?

If the lender posts payments in the bi‑weekly schedule (26 payments/year) or you end up making the equivalent of 13 monthly payments per year, you will pay principal faster and save interest compared to 12 monthly payments. The exact savings depend on how the lender applies interest and whether they accept partial principal reductions without fees.

Is the calculator exact for every lender?

No. This model uses standard discrete amortization mathematics and assumes payments reduce principal immediately. Lender rules (daily interest accrual, payment posting time, escrow handling, rounding, and prepayment penalties) can change real results. Use generated numbers as an accurate mathematical estimate, not a lender payoff statement.

How should I interpret the one‑time reduction field?

One‑time reduction is modelled as an immediate principal payment at time zero. If your one‑time payment happens later, the impact will be smaller; modelling later one‑time payments requires stepwise amortization and is not covered by the closed‑form single‑period equations used here.

Are there regulatory or security standards behind this tool?

This tool follows software quality and security best practices guidance. For privacy and secure handling of inputs, see the NIST Cybersecurity and data handling guidance linked below. For software quality and verification guidance, see cited ISO and IEEE standards. This calculator is informational and not financial, legal, or tax advice.

Sources & citations