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

401k 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 determines your annual contribution based on salary percentage. It then adds the employer match (up to the limit specified). Finally, it applies the Future Value of an Annuity formula with compounding interest to project the balance at retirement.

Test cases

Default input regression check

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

Inputs

  • Contribution Limit Preset: irs_retirement_limits_2026
  • Annual Salary: $75,000
  • Your Contribution: 6%
  • Manual 401(k) Limit: $24,500
  • Employer Match: 3%
  • Annual Return: 7%
  • Years to Grow: 30

Expected outputs

  • Projected Balance: $637,610.31
  • Your Contributions: $135,000.00
  • Employer Contributions: $67,500.00

Known limitations

  • Does not account for salary increases over time or IRS contribution limit changes. Assumes constant salary and return.

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

  • Contribution Limit Preset accepts one of the configured options.
  • Annual Salary accepts values in $.
  • Your Contribution accepts values in %.
  • Manual 401(k) Limit accepts values in $.
  • Employer Match accepts values in %.
  • Annual Return accepts values in %.
  • Years to Grow accepts numeric values.
  • Projected Balance is displayed as currency.
  • Your Contributions is displayed as currency.
  • Employer Contributions 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.

Version history

1.0.0 - 2026-05-06

Generated accuracy and testing page from the current 401k-calculator calculator definition.

Change log

2026-05-06

Published default regression test documentation and metadata fallbacks for 401k 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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