100.00 before tax at 8.25%
100 × 8.25 ÷ 100 = 8.25
The tax is 8.25. Add it to the pre-tax amount to get a total of 108.25. The 8.25% rate here is an example, not a location-based recommendation.
One amount, one tax rate
Sales Tax Calculator
Add tax to a price, or find the tax included in a total. Enter your own rate and see a breakdown that adds up to the cent.
Calculate sales tax
Total including tax
Enter an amount and a tax rate, then select Calculate.
- Pre-tax amount
- Tax amount
- Total including tax
- Tax rate
Pre-tax amount + tax = total:
Amounts are in your input currency with exactly 2 decimal places. ≈ marks rounding. Press Enter to calculate. Successful results appear in this tab's Recent calculations.
Worked examples
120.00 including tax at 20%
120 × 20 ÷ (100 + 20) = 20
The included tax is 20.00, leaving 100.00 before tax. Subtracting 20% of 120 would give 96, which is not the original pre-tax amount.
0.03 including tax at 20%
0.03 × 20 ÷ 120 = 0.005
The exact tax is half a cent. This tool rounds the tax up to 0.01 and subtracts it from 0.03, leaving 0.02. The displayed components satisfy 0.02 + 0.01 = 0.03.
Formulas, rounding, and limits
Let N be the pre-tax amount, G the tax-inclusive total, and r the rate as a percentage (enter 8.25 for 8.25%). Before rounding:
Add: tax = N × r ÷ 100 · G = N + tax
Remove: tax = G × r ÷ (100 + r) · N = G ÷ (1 + r ÷ 100)
The tax is calculated with exact integer fractions and then rounded once to the nearest hundredth; a halfway amount rounds up. In add mode, the entered pre-tax amount is preserved and the rounded tax is added. In remove mode, the entered inclusive total is preserved and the rounded tax is subtracted. The three displayed monetary amounts therefore always reconcile. The derived amount may differ from independently rounding its unrounded formula at a half-cent boundary. The ≈ symbol identifies values changed by this rounding policy.
This model uses 100 minor units per monetary unit and displays exactly 2 decimal places. It does not model currencies with a different number of minor units, cash rounding to coin denominations, or invoice rules that round each item separately. For example, adding 10% tax separately to three items priced 0.05 gives 0.03 total tax with this rounding rule, while taxing their combined 0.15 gives 0.02. A real invoice or tax return may follow different local rules.
The amount can have up to 15 digits before the decimal point and 2 after it. The rate can have up to 10 decimal places and must be between 0% and 1,000%; the upper bound is an input limit, not a statement about legal tax rates. Each input accepts at most 64 characters. Zero amounts and zero rates are allowed. Negative amounts, expressions, currency symbols, percent signs, and scientific notation are not accepted.
This is an arithmetic aid for one amount taxed at one rate. It does not determine liability, handle tax exemptions, choose whether shipping or discounts are taxable, calculate compound taxes, prepare a return, or validate the rate you enter. Combining rates is appropriate only when they apply to the same base without compounding. The same percentage formulas can describe a single VAT or GST component when their assumptions fit, but jurisdiction-specific invoicing and rounding rules remain separate.
References: ASIC Moneysmart — GST calculator demonstrates adding a 10% tax and extracting its included component by dividing the total by 11. California Department of Tax and Fee Administration — Applying Tax to Your Sales and Purchases explains that taxable items, rates, and included-tax pricing depend on applicable rules. These sources provide examples; this calculator does not automatically apply either jurisdiction's rules.
Common questions
Why can I not remove tax by subtracting the tax percentage?
The percentage is applied to the pre-tax amount, not to the larger inclusive total. At 20%, the total represents 120% of the base. Divide by 1.2 to recover that base, or multiply the total by 20 ÷ 120 to find its tax component.
Does the calculator know my local sales tax rate?
No. It uses only the rate you type. Rates and exemptions can vary by location, item, and date. Check the applicable tax authority and ensure that all of the amount entered is subject to the same rate.
Can I use it for VAT or GST?
The add/remove percentage formulas also work for one tax applied to the full base at a single rate. The calculator does not implement local VAT or GST rules, tax credits, mixed supplies, or invoice rounding requirements.
Why is the result different from my receipt?
A receipt may round per item, combine items subject to different rates, or handle discounts and delivery charges differently. This tool rounds tax once on the one amount you enter. It also assumes two decimal places and does not round a cash payment to the nearest coin.
Will switching modes always recover the original amount?
The unrounded formulas are inverses, but cent rounding can lose information. For example, removing 100% included tax from 0.01 rounds the tax to 0.01 and leaves a pre-tax amount of 0.00. Adding tax to that 0.00 cannot recreate the original total. The entered amount is always kept unchanged in the selected mode.