Last updated 23 August 2026
Why "remove tax" isn't just subtraction
If a $118 total includes 18% tax, the tax isn't 18% of $118 — that would overcount it. The pre-tax amount is $118 ÷ 1.18 = $100, and the tax is the $18 difference. Applying the rate to the wrong base is the most common mistake in reverse tax calculations, which is exactly what this mode avoids.
Common questions
Why isn't the tax just the total minus the pre-tax amount divided evenly?
Removing tax from a tax-inclusive total isn't the same as dividing by the rate — dividing a total by (1 + rate) gives the pre-tax amount correctly, but simply subtracting rate% of the total overstates the tax, since that rate applies to the smaller pre-tax figure, not the total.
Does this work for VAT and GST, not just US sales tax?
Yes — the maths is identical regardless of what the tax is called locally. Just enter the applicable rate for VAT, GST, or sales tax.
When would I use "remove tax" instead of "add tax"?
When you have a final, tax-inclusive price — like a receipt total — and need to know how much of it was the actual product cost versus tax, for bookkeeping or expense claims.