Guide · Working backwards
Reverse Percentage Calculator
Updated: June 2026
Most percentage questions start with the whole and ask for a part. A reverse percentage flips that around: you know the part, or the after-figure, and you want the original whole. It is the maths behind "what was the price before the sale?" and "what's the amount before tax?" — and getting the direction of the division right is everything.
Free · No upload · Instant in the browser
The basic reverse formula
If an amount is P% of an unknown total, recover the total by dividing:
For example, 30 is 15% of what? 30 ÷ 0.15 = 200. The intuition: a percentage scaled the original down to your amount, so dividing by that same percentage scales it back up. Whenever you see a part and the percentage it represents, this single division gets you home.
Price before a discount
Here the sale price is what's left after a reduction, so the after-figure represents (100 − discount)% of the original. Divide by that surviving fraction. A jacket on sale for 90 at 25% off: the 90 is 75% of the original, so 90 ÷ 0.75 = 120. The pre-sale price was 120. Dividing by 0.25 instead — a tempting mistake — would wildly overshoot.
Removing tax to find the net
Tax works the opposite way: the price you pay is more than the net, because tax was added on top. So the gross price represents (100 + tax)% of the net. Divide by one plus the rate. A receipt of 120 including 20% VAT has a net of 120 ÷ 1.20 = 100, and the VAT itself is the 20 that remains. Never subtract 20% of the gross — that gives 96, which is wrong, because the 20% was calculated on the smaller net figure.
| Scenario | Divide by | Example |
|---|---|---|
| P% of unknown | P ÷ 100 | 30 ÷ 0.15 = 200 |
| After a 25% discount | 0.75 | 90 ÷ 0.75 = 120 |
| After a 20% increase | 1.20 | 120 ÷ 1.20 = 100 |
| Remove 20% tax | 1.20 | 120 ÷ 1.20 = 100 |
The rule of thumb
Ask one question: was the percentage added or taken away to reach the figure you have? If added (a markup, tax, or increase), divide by 1 + rate. If taken away (a discount or decrease), divide by 1 − rate. If your figure is simply stated as "P% of the total", divide by the rate itself. Picking the right one of these three is the whole skill.
Where you'll use it
- Finding a product's list price from a discounted ticket.
- Splitting a tax-inclusive total into net and tax.
- Recovering a budget or target from a reported percentage of it.
- Backing out a pre-increase salary or rent from the new figure.
Frequently asked questions
How do I find the original number from a percentage?
If an amount is P% of an unknown total, divide the amount by P as a decimal. 30 being 15% of a number means 30 ÷ 0.15 = 200.
How do I find the price before a discount?
Divide the sale price by one minus the discount rate. A 25%-off price of 90 came from 90 ÷ 0.75 = 120.
How do I remove tax to find the net price?
Divide the tax-inclusive price by one plus the tax rate. A 20%-VAT price of 120 has a net of 120 ÷ 1.20 = 100.
Why can't I just subtract the percentage?
Because the percentage was calculated on the original, smaller (or larger) base — not on the figure you already have. Division reverses it correctly; subtraction does not.