Mortgage Payment Calculator with Bi-Weekly Payments
This calculator estimates mortgage payment outcomes when you pay at different frequencies, including bi‑weekly (26 payments per year). Enter the home price and down payment (or use the loan amount directly), the APR, term, frequency, and any extra principal you plan to add each period.
Results include the scheduled payment (no extra), the payment with extra principal, an estimate of how many periods until payoff when paying extra, total estimated paid, and estimated interest saved compared with the original schedule. Use the tool for planning and comparing strategies; final payoff timing can vary due to rounding, lender rules, and payment application timing.
Governance
Record 2803d6a73d8b • Reviewed by Fidamen Standards Committee
Inputs
Results
Loan principal (after down payment)
$240,000.00
Periodic interest rate
0.0015
Scheduled number of periods
780
Scheduled payment per period (no extra)
$528.58
Payment per period (with extra principal)
$528.58
Estimated number of periods to payoff (with extra)
780
Estimated total paid (principal + interest) with extra
$412,295.62
Estimated total interest paid (with extra)
$172,295.62
Total paid under original schedule (no extra)
$412,295.62
Estimated interest savings (vs original schedule)
$0.00
| Output | Value | Unit |
|---|---|---|
| Loan principal (after down payment) | $240,000.00 | USD |
| Periodic interest rate | 0.0015 | — |
| Scheduled number of periods | 780 | — |
| Scheduled payment per period (no extra) | $528.58 | USD |
| Payment per period (with extra principal) | $528.58 | USD |
| Estimated number of periods to payoff (with extra) | 780 | — |
| Estimated total paid (principal + interest) with extra | $412,295.62 | USD |
| Estimated total interest paid (with extra) | $172,295.62 | USD |
| Total paid under original schedule (no extra) | $412,295.62 | USD |
| Estimated interest savings (vs original schedule) | $0.00 | USD |
Visualization
Methodology
The calculator uses standard amortization mathematics: the periodic rate equals the APR divided by the number of payments per year, and the scheduled payment is calculated from the annuity formula for a fixed-rate loan.
When extra principal is added each period, the number of periods required to amortize the loan reduces. The estimate for periods to payoff is derived from the algebraic inversion of the amortization recurrence (logarithmic solution). Results are numerical estimates and assume payments are applied immediately to principal and interest in the stated frequency.
This tool follows software quality and numeric accuracy guidance and cites applicable standards to help ensure trustworthy output. Calculations are subject to floating point rounding consistent with common IEEE 754 implementations.
F.A.Q.
Does bi‑weekly always save interest vs monthly?
Bi‑weekly payment plans can save interest because you make the equivalent of one extra monthly payment per year (26 bi‑weekly payments ≈ 13 monthly payments). Savings depend on whether your lender applies payments to principal immediately and how they treat amortization; this calculator assumes immediate principal reduction.
Is bi‑weekly the same as semi‑monthly?
No. Bi‑weekly means every two weeks (26 payments per year). Semi‑monthly refers to twice a month (24 payments). The timing difference affects interest calculations and payoff speed.
How accurate are the payoff estimates with extra payments?
Estimates use closed‑form algebraic formulas assuming constant payment_with_extra and immediate application to principal. Actual payoff may differ due to payment timing, lender rounding, escrow changes, fees, or payment application policies. See accuracy caveats below.
Should I use APR or periodic rate from my lender?
Use the APR (annual interest rate) reported by the lender for this calculator. If your loan documents provide a periodic nominal rate, that rate divided by payments per year should match APR for fixed-rate loans; disclose differences to your lender if unclear.
Sources & citations
- NIST - Numerical methods and software quality information — https://www.nist.gov
- IEEE - Floating‑point arithmetic standards (IEEE 754) — https://www.ieee.org
- ISO - Standards for quality management and software processes — https://www.iso.org
- OSHA - Workplace safety and engineering standards (for development processes) — https://www.osha.gov
- Consumer Financial Protection Bureau - Mortgage basics — https://www.consumerfinance.gov
- CFPB — Understand Loan Options — https://www.consumerfinance.gov/owning-a-home/loan-options/
- CFPB — Explore Interest Rates — https://www.consumerfinance.gov/owning-a-home/explore-rates/
- Fannie Mae — Loan Terms Glossary — https://www.fanniemae.com/glossary
Further resources
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: 2803d6a73d8bWhat changed (latest)
v1.0.0 • 2025-11-12 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
What changed (latest)
v1.0.0 • 2025-11-12 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Engine
v1.0.0
Data
Baseline (no external datasets)
Content
v1.0.0
UI
v1.0.0
Governance
Last updated: Nov 12, 2025
Reviewed by: Fidamen Standards Committee (Review board)
Credentials: Internal QA
Risk level: low
Reviewer profile (entity)
Fidamen Standards Committee
Review board
Internal QA
Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person
Semantic versioning
- MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
- MINOR: New features or fields that do not change existing outputs for the same inputs.
- PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.
Review protocol
- Verify formulas and unit definitions against primary standards or datasets.
- Run golden-case regression suite and edge-case suite.
- Record reviewer sign-off with credentials and scope.
- Document assumptions, limitations, and jurisdiction applicability.
Assumptions & limitations
- Uses exact unit definitions from the Fidamen conversion library.
- Internal calculations use double precision; display rounding follows the unit's configured decimal places.
- Not a substitute for calibrated instruments in regulated contexts.
- Jurisdiction-specific rules may require official guidance.
Change log
v1.0.0 • 2025-11-12 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: ead12e4c0d2f