Auto Loan Amortization Calculator
This amortization tool estimates payments and interest for auto loans under three common schedules: standard monthly, converted bi‑weekly (24 payments per year by halving the monthly payment), and true bi‑weekly (26 payments per year with payments every 14 days). It includes down payment, trade‑in, and financed fees to show the principal actually amortized.
Results are intended for planning and comparison. Use exact lender disclosures (loan agreement or Truth in Lending statement) for contract terms and legally binding numbers. This tool documents assumptions and calculation methods to improve transparency.
Governance
Record 4090be3faebd • Reviewed by Fidamen Standards Committee
Payments every 14 days (26 payments per year). Because there are 26 payments, this schedule typically reduces principal faster and shortens term versus monthly or 24‑payment bi‑weekly.
Inputs
Advanced inputs
Advanced options
Results
Bi‑weekly payment (26/yr)
-$0.44
Number of payments
130
Total paid
-$57.69
Total interest
-$30,057.69
| Output | Value | Unit |
|---|---|---|
| Bi‑weekly payment (26/yr) | -$0.44 | USD |
| Number of payments | 130 | — |
| Total paid | -$57.69 | USD |
| Total interest | -$30,057.69 | USD |
Visualization
Methodology
We compute a financed principal equal to vehicle price minus down payment and trade‑in plus any financed fees. Periodic rates convert the APR to the payment period (monthly: APR/12; bi‑weekly: APR/26). The standard annuity formula is used to compute fixed periodic payments.
Three scenarios are calculated separately so you can compare: monthly amortization, converted bi‑weekly (monthly payment divided by two; 24 payments/year), and true bi‑weekly (26 payments/year using the bi‑weekly period rate). The true bi‑weekly schedule normally reduces interest and shortens the effective term because it results in extra principal paid each year.
Where interest rate is zero, payments are principal divided by number of payments. Rounding to cents is shown as an optional display choice; underlying math uses periodic rates and exact counts.
Worked examples
Example A: $30,000 vehicle, $0 down, 5% APR, 5 years. Monthly payment computed by monthly formula. True bi‑weekly uses period = APR/26 and 130 payments (5*26), which typically lowers total interest vs monthly.
Example B: Same loan but using converted bi‑weekly (monthly/2) produces 24 payments/year; this does not create extra annual principal reduction compared with monthly schedule and is usually similar to monthly amortization in total interest.
F.A.Q.
What is the difference between converted bi‑weekly and true bi‑weekly?
Converted bi‑weekly splits the monthly payment in half and results in 24 payments per year. True bi‑weekly makes a payment every 14 days (26 payments/year), which yields two extra half‑payments per year and typically reduces principal faster and lowers total interest.
Are fees included in the loan balance?
This tool includes financed fees (taxes, registration, add‑ons) when you enter them. If your lender pays fees separately or charges them outside the financed amount, adjust inputs to match the lender's disclosure for an accurate comparison.
How accurate are the results?
Calculations use standard annuity formulas and documented assumptions. Results are estimates — they do not replace lender disclosures. Rounding, lender timing conventions (business day processing), and day count conventions can produce small differences. See citations to standards for guidance on numerical practices.
What if the APR is zero?
If APR is zero, the tool effectively distributes principal equally over the number of payments (payment = principal / N). This avoids division by zero in practice; exact lender schedules should be used where available.
Can I use this to produce an amortization schedule?
This tool provides period payment amounts, number of payments, and aggregate interest. A full per‑payment amortization schedule (principal/interest split per payment and running balance) is available in dedicated amortization exporters or spreadsheets and should be used for payment timing details.
Sources & citations
- National Institute of Standards and Technology — Numerical Methods and Best Practices — https://www.nist.gov
- International Organization for Standardization — ISO numeric and quality standards — https://www.iso.org
- IEEE — Floating point and numerical accuracy recommendations — https://www.ieee.org
- Occupational Safety and Health Administration (OSHA) — General guidance (regulatory reliability practices) — 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: 4090be3faebdWhat changed (latest)
v1.0.0 • 2025-11-04 • 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 • 2025-11-04 • 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 4, 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 • 2025-11-04 • 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: 5093e1a0b1e7
- 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