Home Loan Amortization Calculator
This calculator compares standard monthly amortization with bi‑weekly payment strategies. It supports a calculated bi‑weekly schedule (26 payments per year) and the common household practice of paying half the monthly payment every two weeks. Enter the loan amount, annual interest rate, and term to see payment amounts, estimated payoff time, and estimated interest paid.
Results are estimates based on mathematical amortization under constant interest and fixed payments. Actual results from a lender may differ because of payment application order, partial‑period interest, rounding, escrow, fees, and local regulatory or lender policies.
Governance
Record 65f788cfa7d7 • Reviewed by Fidamen Standards Committee
Direct comparison: scheduled monthly payments versus paying half the scheduled monthly amount every two weeks. Shows estimated interest savings and time saved. Uses the same amortization formulas and standard compounding assumptions.
Inputs
Results
Scheduled monthly payment
$1,432.25
Half monthly payment (paid bi‑weekly)
$716.12
Estimated interest savings
$33,830.07
Estimated years saved
4.1246
Total interest (half monthly paid bi‑weekly)
$181,778.45
| Output | Value | Unit |
|---|---|---|
| Scheduled monthly payment | $1,432.25 | USD |
| Half monthly payment (paid bi‑weekly) | $716.12 | USD |
| Estimated interest savings | $33,830.07 | USD |
| Estimated years saved | 4.1246 | years |
| Total interest (half monthly paid bi‑weekly) | $181,778.45 | USD |
Visualization
Methodology
Calculations use standard amortization formulas with periodic compounding. Monthly calculations use the monthly periodic rate (annual_rate/12). Bi‑weekly calculations use a periodic rate with 26 periods per year (annual_rate/26).
For accelerated bi‑weekly or half‑monthly practices we compute the number of periods required to amortize the loan using the logarithmic solution for n when payment p satisfies p = P*i/(1 - (1+i)^-n). Where helpful, we convert periods to years by dividing by 12 (monthly) or 26 (bi‑weekly).
Worked examples
Example: $300,000 principal, 4.0% APR, 30 years. Scheduled monthly payment calculates to the standard mortgage payment. Paying half that amount bi‑weekly typically reduces total interest and shortens payoff because it results in 26 half‑payments per year (equivalent to 13 full monthly payments).
Example: If you add a fixed extra $100/month, the tool recalculates the effective payoff time and interest using the net payment per period in the logarithmic formula shown above.
F.A.Q.
Does paying bi‑weekly always save interest?
Paying bi‑weekly can save interest relative to strict monthly payments when it results in more paid principal over a year (for example, 26 half‑payments equals 13 full monthly payments per year). Savings depend on exact payment amounts, payment timing, and how the lender applies each payment.
Are these numbers exact to my loan?
These are mathematical estimates. Lenders may apply payments differently (daily interest accrual, rounding rules, escrow demands, fees). Use results for planning only and consult your loan statement or lender for precise payoff figures.
What is the difference between accelerated bi‑weekly and simply paying half monthly every two weeks?
Accelerated bi‑weekly sets a bi‑weekly payment sized to amortize the loan over the original term with 26 periods per year. Paying exactly half the monthly payment every two weeks often results in faster payoff because it amounts to 13 monthly payments per year, but the exact effect depends on interest compounding and lender application.
How accurate is the calculator and what standards guide it?
Calculation logic follows standard annuity and amortization formulas widely used in finance. For numerical reliability, implementations should follow industry best practices for numeric stability and rounding. Consult standards such as NIST recommendations for numerical computing practices and apply secure coding guidance from ISO/IEEE when integrating into production systems.
Sources & citations
- NIST — Numerical Algorithms and Standards — https://www.nist.gov
- ISO — Quality and Security Standards (general reference) — https://www.iso.org
- IEEE — Coding and Engineering Best Practices (general reference) — https://www.ieee.org
- OSHA — Workplace Financial Tool Guidance (general reference) — https://www.osha.gov
- CFPB Regulation Z — 12 CFR § 1026.22 Determination of Annual Percentage Rate — https://www.consumerfinance.gov/rules-policy/regulations/1026/22/
- CFPB Appendix J — Annual Percentage Rate Computations for Closed-End Credit — https://www.consumerfinance.gov/rules-policy/regulations/1026/j/
- CFPB Annual Percentage Rate Tables — https://www.consumerfinance.gov/compliance/compliance-resources/other-applicable-requirements/annual-percentage-rate-tables/
Further resources
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: 65f788cfa7d7What changed (latest)
v1.0.0 • 2025-11-11 • 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 • 2025-11-11 • 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 11, 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 • 2025-11-11 • 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: 25c9880708eb
- https://www.consumerfinance.gov/compliance/compliance-resources/other-applicable-requirements/annual-percentage-rate-tables/
- https://www.consumerfinance.gov/rules-policy/regulations/1026/22/
- https://www.consumerfinance.gov/rules-policy/regulations/1026/j/
- https://www.ieee.org
- https://www.iso.org
- https://www.nist.gov
- https://www.osha.gov