Business & eCommerceGenerated accuracy model review: 2026-05-06

Sales Tax / VAT 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

1. **Add Tax**: Total = Net * (1 + Rate/100). 2. **Remove Tax**: Net = Gross / (1 + Rate/100). Tax = Gross - Net.

Test cases

Default input regression check

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

Inputs

Price Amount: $100
Tax Rate: 20%
Action: Add Tax (Net -> Gross)

Expected outputs

Final Amount: $120.00
Tax Amount: $20.00
Base Amount: $100.00

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

This calculator applies one flat tax rate to the full amount you enter.
It does not model tax-exempt line items, tiered tax rules, or multi-rate invoices.
Amounts must be non-negative, and the tax rate must be zero or greater.

Unit handling

Price Amount accepts values in $.
Tax Rate accepts values in %.
Action accepts one of the configured options.
Final Amount is displayed as currency.
Tax Amount is displayed as currency.
Base Amount 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 sales-tax-vat-calculator calculator definition.

Change log

2026-05-06

Published default regression test documentation and metadata fallbacks for Sales Tax / VAT.

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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