Last updated 3 September 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.
Tax-exclusive and tax-inclusive pricing
Most confusion with sales tax comes from not knowing which direction you are working in. In the United States, listed prices are almost always tax-exclusive: the shelf says $40, tax is added at the register, and 8.5% tax makes the total $43.40. In most of Europe, the UK, Australia and much of Asia, displayed prices are tax-inclusive: the label says £48 and the VAT or GST is already inside it.
The reverse calculation is where people get it wrong. To pull 20% VAT out of a £48 inclusive price you do not take 20% of £48. You divide by 1.20, which gives £40 net and £8 of tax. Taking 20% of the gross figure would give £9.60 and a net of £38.40, which is wrong by more than a pound and a half on a single item.
A worked example
Say you invoice a client $1,250 for design work in a state with 7.25% sales tax on that service. Tax-exclusive, the tax is $90.63 and the invoice total is $1,340.63. If instead the client agreed a flat $1,250 including tax, your net revenue is $1,250 ÷ 1.0725 = $1,165.50, and $84.50 goes to the state. Same headline number, $84.50 difference in what you actually keep.
Rates themselves vary far more than people expect. In the US, a state rate is often topped up by county, city and special district rates, so two addresses a mile apart can carry different totals. Always confirm the combined rate for the specific delivery address rather than assuming the state figure.
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.
How do I remove tax from a price that already includes it?
Divide by 1 plus the rate as a decimal, not by taking a percentage of the total. For 20% tax on an inclusive price of 48, the net is 48 ÷ 1.20 = 40 and the tax is 8. Taking 20% of 48 gives 9.60, which overstates the tax every time.
Why do two nearby addresses have different sales tax rates?
In the United States a state rate is frequently combined with county, city and special district rates. Those boundaries do not follow postcodes neatly, so the combined rate is determined by the exact delivery address rather than the general area.
Is VAT the same thing as sales tax?
Not quite. Sales tax is collected once, at the final sale to a consumer. VAT and GST are collected at every stage of the supply chain, with businesses reclaiming what they paid on inputs. The arithmetic on a single consumer purchase looks the same, but the systems behind them differ.