Sales Tax Calculator

Worked example

Example: a $120 item with 8.25% sales tax adds $9.90 in tax for a total of $129.90. In remove-tax mode, a $129.90 total at 8.25% includes about $9.90 tax on a $120 base price.

How it works

Enter a purchase price and sales tax rate. In add-tax mode, tax is calculated on the pre-tax price to find the total. In remove-tax mode, the tax embedded in a tax-inclusive price is backed out to find the pre-tax amount. Rounding follows standard currency math.

Limitations

Results are estimates for educational purposes and are not tax advice. Local rates and rules vary. Confirm amounts with an official source.

Privacy and file handling

Your data stays on your device and is not uploaded.

Accuracy & methodology

This section documents how the calculator works, what it leaves out, and when results were last reviewed. Figures are educational estimates—not professional advice—and are not labeled "current" unless tied to automatically updated reference data.

Formula source or methodology

Tax amount = price × rate%. Total = price + tax (or reverse calculation when solving for pre-tax from total).

Jurisdiction

User-defined locality (no US state/local rate database)

Unit system

Currency; percent

Rounding method

Currency amounts round to two decimal places (half up via Math.round × 100 / 100).

Assumptions

• Single combined sales tax rate entered by the user
• Tax applies to the full entered price

Known omissions

• Not tax, legal, investment, or lending advice. Confirm material decisions with qualified professionals.
• State, county, city, and special district rate stacks
• Tax holidays, exemptions, and B2B resale certificates
• Use tax and marketplace facilitator rules

Test cases (automated)

• $100 at 8% → $8 tax and $108 total
• Negative price is rejected

Version & last verified

Logic version 1.0. Content and formulas last verified 2026-07-24.