Reverse Tax Formula
The reverse tax formula works for sales tax, VAT, GST, HST, and other percentage-based tax-inclusive totals.
Calculator
Calculate tax backwards
$120.00 at 20% Tax: pre-tax $100.00, Tax $20.00.
Estimate only. Verify official rates before filing, invoicing, or making tax decisions.
Calculator
Reverse Tax Formula
Starting rate
20%
Rate setting
Enter the rate you want to use
Last updated
2026-05-14
Formula
How reverse tax calculation works
A tax-inclusive total is the original price multiplied by 1 plus the tax rate. Reversing that multiplication means dividing by the same multiplier: total / (1 + rate). Keep the parentheses around 1 + rate.
Pre-tax Price = Total Price / (1 + Tax Rate)
Tax Amount = Total Price - Pre-tax Price
Example
$120.00 at 20%
- Tax-inclusive total = pre-tax price x 1.20
- Pre-tax price = 120 / 1.20 = 100.00
- Included tax = 20.00
- Check: 100.00 x 1.20 = 120.00
FAQ
Common questions
How do you reverse calculate tax?
Divide the tax-inclusive total by 1 plus the tax rate. For example, with a 20% tax rate, divide the total by 1.20.
What is the reverse tax formula?
Pre-tax price = total price / (1 + tax rate). Tax amount = total price - pre-tax price.
Is this calculator tax advice?
No. This is an educational calculator for estimates. Confirm official rates and rules before filing, invoicing, or relying on the result.
Why does the formula need parentheses?
You need to divide by the full multiplier: 1 plus the tax rate. Write total / (1 + rate), not total / 1 + rate.
How can I check a reverse tax result?
Multiply the pre-tax price by 1 plus the tax rate. The result should match the original tax-inclusive total, apart from small rounding differences.
What rate format should I use in the formula?
Use the rate as a decimal. For 20%, use 0.20 in a formula or 20% in a spreadsheet cell formatted as a percentage.
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