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Finance & LoansGenerated accuracy model review: 2026-05-06
Investment 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 uses the Future Value of an Annuity formula for the monthly contributions and the standard Compound Interest formula for the starting balance. It assumes monthly compounding.
Test cases
Default input regression check
Generated from the checked-in default inputs and calculate function.
Inputs
- Starting Amount: $5,000
- Additional Contribution: 200 $/mo
- Annual Return: 8%
- Investment Length: 10 Years
Expected outputs
- End Balance: $47,687.41
- Total Principal: $29,000.00
- Total Investment Growth: $18,687.41
Known limitations
- Assumes a constant rate of return, which does not happen in real stock markets (volatility).
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
- Starting Amount accepts values in $.
- Additional Contribution accepts values in $/mo.
- Annual Return accepts values in %.
- Investment Length accepts values in Years.
- End Balance is displayed as currency.
- Total Principal is displayed as currency.
- Total Investment Growth 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 investment-calculator calculator definition.
Change log
2026-05-06
Published default regression test documentation and metadata fallbacks for Investment Calculator.
Calculator transparency
Accuracy pages are generated from checked-in calculator definitions and can be upgraded with curated review metadata over time.