Percentage calculator
Pick the calculation and enter your numbers: the result and the formula appear.
What is X% of Y?
20% of 150
30
20 ÷ 100 × 150 = 30
X is what percent of Y?
15 out of 20
75%
15 ÷ 20 × 100 = 75%
Percentage change from A to B
Increase
+5%
(2,100 − 2,000) ÷ 2,000 × 100 = +5%, a multiplier of 1.05
Increase or decrease a number by X%
After the increase
2,060
2,000 × (1 + 3 ÷ 100) = 2,000 × 1.03 = 2,060, a difference of +60
Original value before an increase or a discount
Original value
60
42 ÷ (1 − 30 ÷ 100) = 42 ÷ 0.7 = 60
Percentage points or percent?
Gap
+1 pts
Relative change
+33.33%
4 − 3 = +1 point; (4 − 3) ÷ 3 × 100 = +33.3333%
Successive increases or decreases
An increase as a positive number (10), a decrease as a negative one (−10). Empty boxes are ignored.
Overall change
-1%
Average rate per step
-0.5%
(1 + 10 ÷ 100) × (1 − 10 ÷ 100) = 0.99, that is -1%; average rate: 0.99^(1/2) − 1 = -0.5013%
How to work out a percentage of a number
To work out a percentage of a number, divide the percentage by 100 and multiply by the number: 20% of 150 is 20 ÷ 100 × 150 = 30. With this percentage calculator, type 20 in "Percentage X" and 150 in "Number Y" in the first block; the result appears as you type, with the formula written out using your own figures. The other six blocks answer the related questions: what share one number is of another (15 out of 20 is 75%), the percentage change between two values (2,000 to 2,100 is +5%), an increase or discount applied to a price, the original price before the French soldes, the gap in points between two rates and the effect of several changes in a row. The main limit to keep in mind is that a percentage only means something against its base, so two percentages taken from different bases cannot simply be added together.
The formulas at a glance
A percentage is a fraction out of 100: 20% means 20 per hundred, or 0.20. Nearly every calculation comes down to multiplying or dividing by a multiplier. A 3% rise multiplies by 1.03; a 30% discount multiplies by 0.70. Thinking in multipliers avoids most mistakes, especially when changes follow each other.
| Question | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 20% of 150 = 30 |
| X is what % of Y | X ÷ Y × 100 | 15 out of 20 = 75% |
| Change from A to B | (B − A) ÷ A × 100 | 2,000 → 2,100 = +5% |
| Y increased by X% | Y × (1 + X ÷ 100) | 2,000 + 3% = 2,060 |
| Y decreased by X% | Y × (1 − X ÷ 100) | 59.90 − 30% = 41.93 |
| Before a discount of X% | Final value ÷ (1 − X ÷ 100) | 42 ÷ 0.70 = 60 |
Percentages you meet when living in France
Soldes and promotions
France has two official sales periods a year, the soldes in winter and summer, plus promotions the rest of the year. A jacket at €59.90 with 30% off costs 59.90 × 0.70 = €41.93. A second markdown of 20% on the sale price brings it to 41.93 × 0.80 = €33.54, a total discount of 44%, not 50%. Since 2022 the DGCCRF, the French consumer protection office, requires the crossed-out reference price to be the lowest price charged in the 30 days before the reduction.
Pay rises and payslips
A gross salary (salaire brut) of €2,000 a month rising to €2,100 is a change of +5%. Two rises of 3% in a row multiply pay by 1.03 × 1.03 = 1.0609, so +6.09% over two years. Invoices and quotes in France are often written HT (before VAT); the French VAT calculator turns HT into TTC at 20%, 10%, 5.5% or 2.1%.
School marks out of 20
French schools mark out of 20. A 15 out of 20 is 15 ÷ 20 × 100 = 75% of the points, and 26 out of 40 is 65%. To compare marks on different scales, turn them into percentages first, then multiply by the new scale and divide by 100.
Percentage points and successive changes: two traps
When the quantity is already a percentage (a mortgage rate, an unemployment rate, a VAT rate), its change can be described two ways. The gap in points is a plain subtraction: from 3% to 4% the rate gains 1 point. The relative change divides that gap by the starting rate: 1 ÷ 3 = +33.33%. Both are correct, they just answer different questions.
Successive changes multiply. A 10% rise followed by a 10% fall gives 1.10 × 0.90 = 0.99, a loss of 1%. The average rate per step shown by the tool is the single rate that, repeated, gives the same end result; it is the figure behind phrases such as "on average per year". For pricing, the same confusion of bases separates markup from margin, explained on the profit margin calculator.
Frequently asked questions
A price drops 20% and then rises 20%, am I back where I started?
No, you are 4% down. The drop applies to the starting price and the rise to the lower price: €100 becomes €80, then €80 plus 20% is €96. Successive percentages multiply rather than add up: 0.8 × 1.2 = 0.96. To get back to €100 after a 20% cut you need a 25% rise. The successive changes block shows this when you enter 20 and −20.
A shop in France shows the sale price and the discount, how do I find the original price?
Divide the sale price by what is left after the discount. An item at €42 after 30% off cost 42 ÷ 0.70 = €60 before the soldes. Adding 30% to €42 gives €54.60, which is wrong because the 30% was taken off €60. Since 2022, French shops must base the discount on the lowest price charged in the 30 days before the reduction.
My French mortgage rate went from 3% to 4%, is that a 1% or a 33% rise?
Both figures describe it, but they answer different questions. The rate gained 1 percentage point (4 − 3), which is a relative rise of 33.33% (1 ÷ 3 × 100). Saying the rate rose by 1% would suggest it moved to 3.03%. Banks and the press in France say « 1 point » for the gap; the points block on this page gives both numbers.
How do I turn a French mark out of 20 into a percentage?
Divide the mark by 20 and multiply by 100: 14 out of 20 is 14 ÷ 20 × 100 = 70%. The other way round, multiply the percentage by 20 and divide by 100: 85% is 17 out of 20. French schools and universities grade out of 20, and 10 out of 20 is the usual pass mark, so a 12 is a solid result rather than a weak one.
Can I type numbers with a decimal point or a comma?
Yes. The English page reads 1,250.50 as one thousand two hundred and fifty point five, and also accepts a decimal comma such as 2,5 the way French documents write it. Spaces, the % sign and the € sign are ignored. Results show up to four decimals with a decimal point, while the calculation keeps full precision behind the scenes.
Sources
- Service-public.fr, Soldes : règles à respecter (sales: the rules), page read on 27 October 2026.
- Service Public Entreprendre, Affichage des prix : règles à respecter (price display rules), page read on 27 October 2026.
- DGCCRF, economie.gouv.fr, Soldes 2022 : les nouvelles règles d'affichage des démarques et réductions de prix (new rules for showing reductions), page read on 27 October 2026.
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