Fidamen

Auto Loan APR Calculator

This calculator estimates scheduled loan payments when you select bi‑weekly (26 payments/year) or monthly (12 payments/year) frequency. It supports adding upfront fees to the financed principal and adding a recurring extra payment per period as an estimate of the impact on cash flow and interest.

Results labeled "estimate" use closed‑form amortization formulas and assume the number of scheduled payments remains equal to term_years × periods_per_year. If you add recurring extra payments, the actual payoff date and total interest will usually be lower; determining the exact payoff date requires stepwise amortization and rounding rules which the calculator notes explicitly.

Updated Nov 8, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record efa29304907e • Reviewed by Fidamen Standards Committee

Standard amortization assuming 26 payment periods per year. Extra periodic payments are added to each scheduled payment and shown as an estimate; exact payoff date requires iterative amortization.

Inputs

Results

Updates as you type

Scheduled payment (bi‑weekly)

$180.39

Periodic payment including extra (estimate)

$180.39

Scheduled number of payments

130

Estimated total paid (estimate)

$23,450.50

Estimated total interest (estimate)

$3,450.50

OutputValueUnit
Scheduled payment (bi‑weekly)$180.39USD
Periodic payment including extra (estimate)$180.39USD
Scheduled number of payments130—
Estimated total paid (estimate)$23,450.50USD
Estimated total interest (estimate)$3,450.50USD
Primary result$180.39

Visualization

Methodology

Periodic rate is calculated as APR ÷ periods per year. Scheduled payment uses the standard annuity formula for level payments with that periodic rate and number of payments.

When fees are financed the financed principal increases by the fee amount and payments are recalculated on that principal. Additional periodic payments are added to the scheduled payment and presented as an estimate; exact amortization with extra payments requires iterative decrementing of principal per payment.

Design and numerical considerations follow common best practices for financial calculators. For software quality and numeric handling we recommend alignment with NIST software assurance practices and IEEE numerical stability recommendations; for financial messaging and interoperability consider ISO 20022 guidance.

F.A.Q.

What is APR vs interest rate?

APR (annual percentage rate) is the annualized cost of credit expressed as a percentage. In this calculator APR is treated as the nominal APR and converted to a periodic rate by dividing by the number of payments per year. Some regulatory disclosures require an 'effective APR' that accounts for fees and compounding; this tool shows financed fees separately and provides estimates.

Why do bi‑weekly payments often reduce interest cost?

Bi‑weekly schedules create more frequent compounding and, in practice, correspond to 26 half‑month payments per year. If you keep the same nominal payment cadence (and especially if you make an extra payment each year), you typically reduce principal faster. This calculator shows scheduled bi‑weekly payments and an extra payment estimate; exact interest savings need full amortization.

Are results exact to the cent?

The closed‑form formulas provide precise mathematical results, but real loan schedules depend on rounding rules (per payment rounding, truncation), payment timing, and lender practices. Use results as a reliable estimate. For regulatory disclosures, always use lender‑provided amortization schedule and Truth in Lending Act (TILA) disclosures.

How should I treat fees?

If you choose to finance upfront fees, this tool adds them to the principal and recalculates payments. Many regulations require separate disclosure of finance charges; include financed fees in comparisons but verify required disclosure formats with your compliance team.

What if I want exact payoff date when adding extra payments?

Exact payoff date requires iterative amortization: apply each payment to interest then principal, subtract extra payment each period, and stop when principal ≤ 0. This tool provides an upper‑bound estimate using fixed number_of_payments; for an exact schedule export to a stepwise amortization tool or request a lender amortization schedule.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: efa29304907e

What changed (latest)

v1.0.0 • 2025-11-08 • 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 8, 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 • 2025-11-08 • 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: 5c296a4bd6ab