Auto Loan Amortization Calculator with Bi-Weekly Payments

This calculator models loan amortization for auto loans using a chosen payment frequency (monthly, bi‑weekly, or weekly). It computes scheduled periodic payments, the effect of optional per‑period extra payments and one‑time fees, projected number of payments until payoff, total amount paid, and total interest.

Bi‑weekly schedules (26 payments per year) commonly accelerate principal reduction versus monthly payments because there are effectively 13 full monthly equivalents per year when extras or split‑month strategies are applied. Use the extra payment field to model intentional overpayments per period; use fees to model one‑time costs rolled into the principal.

Updated Nov 27, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record f2f59b952de9 • Reviewed by Fidamen Standards Committee

Computes periodic payment, projected number of payments and payoff time, total amount paid and total interest for a loan given principal, APR, term, payment frequency, optional per‑period extra payment, and one‑time fees. Assumes constant interest rate and level payments per period.

Inputs

Loan amount (principal)

Min 0

Annual interest rate (APR, %)

Min 0 · Max 100

Term (years)

Min 0.1 · Max 30

Payment frequencyExtra payment per period (optional)

Min 0

One‑time fees to add to loan balance (origination, doc fees)

Min 0

Results

Updates as you type

Periodic payment (including extras & pro‑rated fees)

$261.04

Scheduled periodic payment (no extras)

$261.04

Projected number of payments

130

Projected payoff time (years)

Total amount paid (payments sum)

$33,934.77

Total interest paid

$3,934.77

Equivalent monthly payment (for comparison)

—

Output	Value	Unit
Periodic payment (including extras & pro‑rated fees)	$261.04	USD
Scheduled periodic payment (no extras)	$261.04	USD
Projected number of payments	130	payments
Projected payoff time (years)	5	years
Total amount paid (payments sum)	$33,934.77	USD
Total interest paid	$3,934.77	USD
Equivalent monthly payment (for comparison)	—	USD

Primary result$261.04

Visualization

Points

Methodology

The tool assumes a fixed annual percentage rate (APR), level payments per chosen period, and simple amortization (interest calculated on outstanding principal each period). Periodic rate r = APR / 100 / frequency. Total scheduled periods n = term_years * frequency. When r is positive, the scheduled periodic payment is P * r / (1 - (1 + r)^(-n)); when r equals zero, payments are principal divided by n.

Extra per‑period payments reduce the principal faster and thus shorten the number of payments. One‑time fees are pro‑rated across scheduled payments in the periodic payment shown; the calculator then projects the number of payments required to amortize the combined balance given the chosen periodic payment amount.

This calculator includes safeguards that cap or floor computed values to avoid nonsensical outputs (for example negative logarithms). Inputs near edge cases (zero APR, extremely small term, or very large extra payments relative to principal) may require manual validation; see the accuracy and limits section below.

Key takeaways

Use the frequency selector to compare monthly, bi‑weekly, and weekly schedules. Enter any planned extra payment per period and any one‑time fees to see the effect on payoff time and interest.

This calculator is intended for planning and comparison. For contract‑level amortization, consult your lender’s schedule and disclosures.

F.A.Q.

Why does a bi‑weekly schedule pay off faster than monthly?

Bi‑weekly schedules with 26 payments result in the equivalent of 13 monthly payments per year if you make every bi‑weekly payment. That extra half‑month each year reduces principal faster and lowers total interest compared with 12 monthly payments.

How does the calculator treat one‑time fees?

One‑time fees entered are pro‑rated across scheduled payments for the periodic payment displayed and included when projecting total paid and interest. If your lender handles fees differently, enter them into the principal field or adjust accordingly.

What happens if APR is zero?

Zero APR is supported; the scheduled payment becomes principal divided by total scheduled periods. Very low APR values are prone to rounding differences; review results and consider small tolerance adjustments for contracts with atypical compounding.

Are extra payments applied immediately to principal?

Yes. This tool models per‑period extra payments as immediately reducing principal at the time of payment, which shortens the projected amortization schedule and reduces total interest.

How accurate are these results for an actual loan statement?

Results are a projection based on the inputs and standard amortization math. Actual lender schedules may differ due to day‑count conventions, variable compounding, payment‑applied rules, rounding policies, fees timing, or escrow/insurance impounds. Use the calculator for planning and cross‑check with your loan contract.

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 — Loan Terms and Amortization — https://www.consumerfinance.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

Related tools

External guidance

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: f2f59b952de9

What changed (latest)

v1.0.0 • 2025-11-27 • 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

Governance

Last updated: Nov 27, 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 • 2025-11-27 • 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: 73756f2f885a