Percentage Calculator
Three percentage calculations in one tool. Choose the mode, type the two numbers and the result appears straight away.
Results are estimates. Solvemis accepts no responsibility for the results obtained or for how they are used.
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How it works
How to use it
- Choose what you want to calculate: X % of an amount, what percentage one number is of another, or the change between two values.
- Type both numbers the way you normally would.
- The result appears straight away. For a change, the sign shows whether it is a rise (+) or a fall (−).
How it is calculated
A percentage is a fraction of 100: 15 % equals 0.15. X % of Y is X ÷ 100 × Y; what percentage X is of Y is X ÷ Y × 100; and the change from X to Y is always divided by the starting value, never by the end value.
Change = (Y − X) ÷ |X| × 100
Sources
- porcentaje (Diccionario de la lengua española) — Real Academia Española
- NIST Guide to the SI, Chapter 7, section 7.10.2 (Percent) — National Institute of Standards and Technology (NIST)
About this calculator
The three calculations it solves
Almost every percentage question falls into one of these three cases, and the tool covers all three from the same place.
What is X % of Y
The most common: discounts, tips, VAT, commissions. Divide the percentage by 100 and multiply by the amount.
21 % of 450 € = (21 ÷ 100) × 450 = 94.50 €
What percentage is X of Y
Useful for expressing a part of a total: how much an expense weighs on your salary, what share of an exam you got right. Divide the part by the total and multiply by 100.
45 correct out of 60 questions = (45 ÷ 60) × 100 = 75 %
Percentage change from X to Y
Compares two moments: a price rise, how a bill has changed, a change in a metric. Subtract the starting value from the end value, divide by the starting value and multiply by 100.
From 80 € to 92 € = ((92 − 80) ÷ 80) × 100 = +15 %
A negative result means a fall. You always divide by the starting value, never by the end value: that is the most common mistake and it changes the result.
The three mistakes that cost the most money
Chaining percentages as if they added up. Two successive 20 % discounts are not 40 %. On 100 €, the first leaves 80 € and the second takes off 16 €, not 20: the final price is 64 €, a real discount of 36 %. Chained percentages multiply; they don’t add.
Subtracting a percentage to undo it. To get the pre-VAT price from a price with VAT, don’t subtract 21 %: divide by 1.21. On 121 €, subtracting 21 % gives 95.59 €, when the real base is 100 €. The percentage was applied to the base, not to the total.
Mixing percentage points and percentages. It’s the favourite confusion of headlines. Going from 4 % to 6 % unemployment is a rise of 2 percentage points, but also a 50 % increase. Both figures are correct and describe the same thing; using one where the other belongs exaggerates or downplays the figure at will.
Shortcuts that work in your head
- 10 % is moving the decimal point one place to the left. 10 % of 340 is 34.
- 5 % is half of 10 %. 5 % of 340 is 17.
- 1 % is moving the decimal point two places. 1 % of 340 is 3.4.
- With those three you can build almost any other: 15 % is 10 % + 5 %, and 20 % is 10 % twice.
- Percentages are commutative: 8 % of 50 is the same as 50 % of 8, that is, 4. When a calculation resists, flip it round and it usually comes out on its own.
Frequently asked questions
How do you work out X % of an amount?
Divide the percentage by 100 and multiply by the amount. 15 % of 200 is (15 ÷ 100) × 200 = 30.
If something goes up 20 % and then down 20 %, does it return to the original price?
No. A 100 € item that goes up 20 % becomes 120 €, and a 20 % drop on 120 € is 24 €, so it ends at 96 €. Each percentage is applied to a different base.
What is the difference between a percentage point and a percentage?
If an interest rate goes from 2 % to 3 %, it has risen 1 percentage point, but that is a 50 % increase on the previous value. Mixing them up completely changes the size of the figure.
Updated 30 September 2026
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