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Finance & LoansGenerated accuracy model review: 2026-05-06

APR Calculator accuracy and testing

This page documents how Calwarden builds trust for this calculator: source notes, regression-style default tests, limitations, assumptions, unit handling, rounding, and visible change history.

Formula source

  • The calculator first determines the monthly payment based on the nominal interest rate. Then, it subtracts the fees from the loan amount to find the 'Net Loan Proceeds'. Finally, it calculates the interest rate required to pay off the *original loan amount* using the *net proceeds* over the term.

Test cases

Default input regression check

Generated from the checked-in default inputs and calculate function.

Inputs

  • Loan Amount: $200,000
  • Interest Rate: 6.5%
  • Term (Years): 30
  • Extra Fees: $3,000

Expected outputs

  • Real APR: 6.65%
  • Nominal Monthly Payment: $1,264.14

Known limitations

  • Assumes fees are paid upfront and deducted from loan proceeds or added to cash to close. Does not account for interest-only periods.

Assumptions

  • Inputs are interpreted exactly as entered in the calculator form.
  • The calculation runs locally in the browser using the current checked-in calculator definition.

Unit handling

  • Loan Amount accepts values in $.
  • Interest Rate accepts values in %.
  • Term (Years) accepts numeric values.
  • Extra Fees accepts values in $.
  • Real APR is displayed as a percentage.
  • Nominal Monthly Payment is displayed as currency.

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.

Version history

1.0.0 - 2026-05-06

Generated accuracy and testing page from the current apr-calculator calculator definition.

Change log

2026-05-06

Published default regression test documentation and metadata fallbacks for APR Calculator.

Calculator transparency

Accuracy pages are generated from checked-in calculator definitions and can be upgraded with curated review metadata over time.

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