Reverse Sales Tax Calculator
Back the tax out of a total to find the price before tax, and see why subtracting the rate gives the wrong answer.
Result
Enter total including tax to see the result.
https://calcgallery.com/consumption-tax/reverse-sales-tax-calculator/
Results are arithmetic from the amounts and rates you enter. The site publishes no tax rate, threshold or tipping convention, and rates vary by jurisdiction and change. Check the rate on your receipt, invoice or tax authority guidance, and confirm anything that matters with a qualified adviser. Read the full disclaimer
How to use the Reverse Sales Tax Calculator
- Enter the total you paid, including tax.
- Enter the tax rate that applied.
- Read the price before tax and the tax inside it.
- Compare it with what subtracting the rate would have given, and note the gap.
How it is calculated
price before tax = total ÷ (1 + rate)tax = total − price before taxIt is a division, not a subtraction. This is the entire reason the page exists, and the mistake is so natural that the page shows it as an output rather than mentioning it in a footnote.
Why subtracting the rate is wrong
The rate was charged on the pre-tax price. Once you have a total, that price is no longer what you are holding — the total is bigger, so taking the rate off the total removes too much.
| Right | Wrong | |
|---|---|---|
| 108.25 at 8.25% | 100.00 | 99.32 |
| 21.64 at 8.25% | 19.99 | 19.85 |
| 120.00 at 20% | 100.00 | 96.00 |
The error grows with the rate. At 8.25% it is 68 cents on a hundred-dollar purchase. At 20% it is four pounds in a hundred and twenty. At 25% it would be more than six.
The tax share, which also surprises people
The tax inside a tax-inclusive price is not the rate. It is:
share = rate ÷ (1 + rate)At 8.25% that is 7.62% of the total. At 20% it is exactly one sixth — 16.67% — which is the figure HMRC’s VAT Notice 700 calls the VAT fraction. It is always smaller than the rate, for the same reason the subtraction fails: the denominator is the bigger number.
Practical tips
This is the calculation for expense claims and bookkeeping. A receipt often shows only a total, and the net is what goes in the books.
It round-trips exactly. A price taken forward through the sales tax calculator and back through this one returns to itself, to the cent.
The rate must be the one that applied, not today’s rate, if the receipt is old.
A mixed basket needs splitting first. If some items were taxed at a different rate or exempt, back each portion out separately — one rate against a mixed total gives a figure that is right for nothing in it.
At 20%, dividing by six is a decent mental check. The tax in a VAT-inclusive price at the standard UK rate is one sixth of it.
With your numbers
- Subtracting the rate would give $99.32, which is wrong: the rate was charged on the smaller pre-tax price, not on the total
- So the tax inside the total is $8.25, which is 7.6212% of it rather than 8.25%
- $108.25 ÷ 1.0825 = $100.00 before tax
Quick reference
Backing tax out of a total is a division, not a subtraction of the rate. The page shows both so the difference is visible.
| Example | Price before tax |
|---|---|
| 108.25 at 8.25% | $100.00 |
| 21.64 at 8.25% | $19.99 |
| 53.00 at 6% | $50.00 |
| 107.50 at 7.5% | $100.00 |
| 120 at 20% | €100.00 |
| 105 at 5% | €100.00 |
| 1,313.26 at 6.375% | €1,234.56 |
| 100 at 0% | €100.00 |
Common questions about the Reverse Sales Tax Calculator
- Why can I not just subtract the rate?
- Because the rate was charged on the smaller pre-tax price, not on the total you are starting from. Taking 8.25% off 108.25 removes 8.93, but the tax actually in that total is 8.25. The gap is 68 cents on a 108 dollar purchase, and it grows with the rate: at 20% VAT on 120, subtracting gives 96.00 where the real net is 100.00 — four pounds out.
- Why is the tax share smaller than the tax rate?
- Because the two are fractions of different things. The rate is a fraction of the pre-tax price; the share is a fraction of the total, which is bigger. At 8.25% the tax is 7.62% of the total. At 20% it is exactly one sixth, or 16.67% — the figure HMRC calls the VAT fraction. The formula is rate divided by one plus the rate.
- When would I need this?
- Whenever you have a tax-inclusive figure and need the net: expense claims that want the pre-tax amount, bookkeeping from a till receipt that shows only the total, pricing work where you know what you want the shelf price to be, and any VAT or GST jurisdiction, where consumer prices are quoted inclusive by default.
- Does this work for VAT and GST?
- Yes — the arithmetic is identical, because a consumer pays the same headline rate whichever way the tax is collected. The dedicated VAT and GST pages add the parts specific to those systems: the input and output position for a business, and the component split an invoice shows. For simply backing a rate out of a total, this page is the same calculation.
- How accurate is it to the cent?
- Exact, to the limits of the total you enter. The pre-tax figure and the tax are computed from the unrounded division and always reconstruct the total you typed. If you feed a total produced by the sales tax calculator back into this one, you get the original price back to the cent.