Fidamen

Auto Loan Fixed Rate Calculator

This fixed-rate auto loan calculator estimates the monthly payment, total amount paid, and total interest for a straightforward fixed-rate installment loan. It includes sales tax and one-time fees in the financed amount when calculating payments.

Use the fields to enter the vehicle price, down payment and trade-in, any fees, the annual interest rate (APR), and the loan term in months. Results are numerical estimates intended for planning and comparison, not a guarantee of loan terms.

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

Governance

Record fb80f45ea601 • Reviewed by Fidamen Standards Committee

Inputs

Results

Updates as you type

Amount to Finance

$30,050.00

Estimated Monthly Payment

$580.95

Total Paid (Principal + Interest)

$34,857.04

Total Interest Paid

$4,807.04

OutputValueUnit
Amount to Finance$30,050.00USD
Estimated Monthly Payment$580.95USD
Total Paid (Principal + Interest)$34,857.04USD
Total Interest Paid$4,807.04USD
Primary result$30,050.00

Visualization

Methodology

The calculator applies standard amortizing-loan mathematics: a fixed monthly rate derived from the annual rate (APR/12) and the annuity payment formula for level payments. Sales tax and one-time fees are added to the financed amount unless paid separately.

We follow numerical best practices by anchoring calculations to IEEE floating-point principles for arithmetic stability and recommending verification against lender disclosures. Outputs are rounded for presentation but underlying math uses full-precision arithmetic where supported.

Key takeaways

This calculator provides clear estimates for fixed-rate auto loans using standard amortization formulas and includes sales tax and fees in the financed amount by default.

Always compare calculator results to official lender disclosures and consider consulting a loan officer for binding offers. Results are approximate and intended for budgeting and comparison only.

F.A.Q.

Does this calculator use APR or nominal interest rate?

Enter the annual percentage rate (APR) as provided by the lender. APR reflects the nominal rate; this calculator uses the APR to compute periodic interest compounded monthly. It does not add other annualized fees into APR unless you include them in 'fees'.

Will rounding affect the result?

Displayed numbers are rounded for clarity. Under the hood calculations assume full floating-point precision; minor cent-level differences can occur when lenders apply per-payment rounding or different compounding/period conventions.

How do I model a 0% interest offer?

Set Annual interest rate (APR) to 0. The calculator will compute equal principal payments: financed principal divided by the number of months.

Does sales tax always get financed?

By default this tool adds sales tax on the vehicle price to the financed amount. If you plan to pay sales tax up front, set 'sales tax rate' to 0 or subtract the tax from financed amounts before using the tool.

Is this a loan approval or an offer?

No. This is an estimation tool only. Final loan terms, fees, and APR are determined by lenders and contractual disclosures.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: fb80f45ea601

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: 4ba8fcd1c1c8