Used Car Loan Affordability Calculator accuracy and testing

Formula source

• Target monthly payment = income x target ratio. Maximum loan is the present value of that payment over the term and APR.

Test cases

Known limitations

• This page documents the checked-in calculator logic and does not certify results for every real-world edge case.
• Use the result as a planning estimate unless the calculator page states a stricter purpose.

Assumptions

• All prices, fees, rates, and vehicle assumptions are user-entered.
• Calculations run locally in your browser and are not stored by Calwarden.
• This is planning math, not financial, tax, insurance, legal, or mechanical advice.

Unit handling

• Gross Monthly Income accepts values in $/mo.
• Existing Monthly Debt accepts values in $/mo.
• Target Auto Payment Ratio accepts values in %.
• Loan APR accepts values in %.
• Loan Term accepts values in months.
• Down Payment accepts values in $.
• Trade-In Value accepts values in $.
• Tax and Fee Rate accepts values in %.
• Affordable Purchase Price is displayed as currency.
• Target Monthly Payment is displayed as currency.
• Maximum Loan Amount is displayed as currency.
• Debt Ratio After Payment is displayed as a percentage.

Rounding rules

• Number displays use up to 2 decimal places in the calculator UI.
• Currency outputs are displayed with standard US dollar formatting.
• Percent outputs are displayed with two decimal places.
• Input precision follows configured step values where provided.

Version history

Change log