What does a sales tax calculator do?
This tool separates a purchase into a pre-tax subtotal, a sales tax amount, and a final total. Use it when comparing a shelf price with the amount charged at checkout, or when a receipt already includes tax and you want to recover the approximate base price.
Add sales tax to a price
Enter the amount before tax, choose No — add tax, and specify the tax rate. The formula is:
Tax = price × (rate ÷ 100)
Total = price + tax
For example, a $100 taxable purchase at 8% creates $8 tax and a $108 total. A zero rate leaves the subtotal unchanged.
Reverse-calculate a tax-inclusive price
If the amount you enter already includes tax, select Yes — extract tax. Simply subtracting 8% of $108 gives the wrong pre-tax price because the rate applies to the base, not the final total.
Subtotal = tax-inclusive total ÷ (1 + tax rate ÷ 100)
For $108 including 8% sales tax, the subtotal is $100 and tax is $8.
Pre-tax discounts and multiple rates
Apply eligible discounts and determine the actual taxable base before entering a value. In some places, taxes differ by product, local area, shipping or exemptions. This calculator does not automatically look up those laws or combine tax authorities.
Rounding and currency display
Dollar amounts display to cents, but tax treatment and rounding requirements vary. Selecting GBP, EUR, INR or other currency changes the symbol without doing a foreign-exchange conversion. Check receipt rules before making accounting decisions.
Common mistakes
Do not apply the tax rate twice, assume all products are taxable, or reverse inclusive tax using a simple percentage subtraction. Confirm whether your invoice is tax-inclusive, and remember that VAT and GST systems can have different legal conventions from U.S. sales tax.
Go deeper
Read our sales tax formula tutorial for worked examples and differences between inclusive and exclusive pricing.