Mortgage Payment Calculator
This calculator compares a standard monthly mortgage payment schedule to a bi‑weekly schedule that uses 26 payments per year (every two weeks). It shows estimated periodic payments, total interest paid under each schedule, and estimated interest savings when using a true bi‑weekly amortization with 26 payments per year.
Use this tool for planning and comparison only. It assumes a fixed nominal annual interest rate compounded at the payment frequency and does not include taxes, insurance, fees, escrow, changing rates, or lender-specific rounding/processing rules.
Governance
Record f624ac074d21 • Reviewed by Fidamen Standards Committee
Inputs
Results
Monthly payment
$1,432.25
Bi‑weekly payment (26 payments/year)
$660.73
Total interest paid (monthly schedule)
$215,608.52
Total interest paid (bi‑weekly schedule)
$215,369.52
Estimated interest saved (monthly − bi‑weekly)
$239.00
Interest saved (%) versus monthly
11.08%
| Output | Value | Unit |
|---|---|---|
| Monthly payment | $1,432.25 | USD |
| Bi‑weekly payment (26 payments/year) | $660.73 | USD |
| Total interest paid (monthly schedule) | $215,608.52 | USD |
| Total interest paid (bi‑weekly schedule) | $215,369.52 | USD |
| Estimated interest saved (monthly − bi‑weekly) | $239.00 | USD |
| Interest saved (%) versus monthly | 11.08% | % |
Visualization
Methodology
Periodic payment formulas follow the standard amortizing loan formula: payment = r * P / (1 - (1 + r)^-N), where r is the periodic interest rate and N is the total number of payments. Monthly calculations use 12 periods per year; bi‑weekly calculations use 26 periods per year.
Outputs are numerical estimates derived from the user inputs. Where the annual interest rate is zero, the payment reduces to principal divided by the total number of payments. This calculator does not perform lender-specific adjustments, nor does it substitute for a lender payoff quote.
Key takeaways
Bi‑weekly amortization with 26 payments per year commonly reduces total interest versus 12 monthly payments because it increases payment frequency and results in effectively extra payments per year.
Actual lender implementations vary. Some services accept two half‑monthly payments but treat them as a single monthly payment (24 periods per year), which does not produce the same savings as a true 26‑payment bi‑weekly schedule.
Worked examples
Example 1: $300,000 principal, 4.0% APR, 30 years. Monthly payment and bi‑weekly payment are computed using the formulas above; bi‑weekly schedule typically reduces total interest because it results in more frequent compounding periods and effectively makes an extra monthly payment each year (26 half‑payments vs 12 full payments).
Example 2: Zero interest rate: a $100,000 principal over 10 years yields payments of $833.33 monthly or $384.62 bi‑weekly (if using exact division by number of payments).
F.A.Q.
What is the difference between bi‑weekly (26) and semi‑monthly (24) payments?
Bi‑weekly means every two weeks, yielding 26 payments per year. Semi‑monthly means twice per month on fixed dates, yielding 24 payments per year. A true 26‑payment bi‑weekly plan typically reduces interest more than a 24‑payment plan because it results in an extra full monthly payment over the year.
Does this calculator include taxes, insurance, or escrow?
No. This tool calculates principal and interest only. Add taxes, insurance, HOA fees, and other charges separately to estimate total monthly housing cost.
Are results exact for my loan payoff?
No. Results are estimates based on mathematical amortization. Lender rounding, payment application order (interest vs principal), fees, prepayment penalties, and differing compounding/statement rules will affect your actual payoff. Always request a payoff quote from your lender.
What assumptions could invalidate these estimates?
Assumptions include: fixed nominal rate for the full term, no additional principal prepayments except as modeled, interest calculated at the specified periodic frequency, and no lender rounding or fees. Adjustable‑rate mortgages, escrow advances, and payment holidays will alter real results.
Sources & citations
- National Institute of Standards and Technology (NIST) — https://www.nist.gov
- International Organization for Standardization (ISO) — https://www.iso.org
- Institute of Electrical and Electronics Engineers (IEEE) — https://www.ieee.org
- Occupational Safety and Health Administration (OSHA) — https://www.osha.gov
- Consumer Financial Protection Bureau — Mortgage basics and disclosures — 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: f624ac074d21What changed (latest)
v1.0.0 • 2025-11-30 • 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 • 2025-11-30 • 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 30, 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 • 2025-11-30 • 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: d52e309f4434