Sales Tax Calculator
Add sales tax to a price, or work backwards from a tax-inclusive total to find the original price.
Last updated · View algorithm, constants and default inputs (JSON)
Breakdown
About this calculator
Sales tax is charged on the price of the goods, not on the tax itself. This calculator works in both directions, so you can check a receipt as easily as you can total up a purchase.
Worked example
calculated with the default values below
Amount 100 $ · Sales tax rate 8.5 % · Calculation Add tax to amount Price before tax 100.00 $ · Sales tax 8.50 $ · Total with tax 108.50 $
General background references
Disclaimer
These calculators give estimates for general information only. They are not financial, tax or investment advice and do not take your personal circumstances into account. Before borrowing, investing or filing, confirm the numbers with a qualified adviser in your jurisdiction.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
m = 0 → T = A(1 + r ÷ 100); m = 1 → N = A ÷ (1 + r ÷ 100); m ∈ {0,1}
- A
- Entered amount
- r
- Tax rate (%)
- m
- Mode: 0 add tax, 1 remove tax
- T
- Gross total with tax
- N
- Net before tax
Add mode: tax = A × r ÷ 100. Remove mode: tax = A - N; the amount is treated as already tax-inclusive.
Frequently asked questions
Why does removing tax divide by one plus the rate?
To strip tax from a final total you divide by one plus the rate, not subtract the rate, because the tax was computed on the pre-tax amount. A 100 dollar total at 8.5 percent therefore yields about 92.17 dollars net and 7.83 dollars tax, whereas adding tax to 100 dollars gives 8.50 dollars tax and 108.50 total. The two directions answer different receipt questions, and the rate is entered as a percent, not a decimal.