How to Calculate Percentages (the Easy Way)
A percentage is just a fraction out of 100 — "per cent" literally means "per hundred". Once you see that, every percentage problem becomes one of a few simple patterns. Here are the ones you actually use, with the steps for each.
What is X% of a number?
To find a percentage of a number, turn the percent into a decimal (divide by 100) and multiply. For 20% of 150: 20 ÷ 100 = 0.20, then 0.20 × 150 = 30. A handy shortcut: 10% of any number is just that number with the decimal point moved one place left, and you can build other percentages from there.
📊Calculate any percentage instantlyPercentage Calculator →X is what percent of Y?
To express one number as a percentage of another, divide the part by the whole and multiply by 100. If 30 out of 150 questions were correct: 30 ÷ 150 = 0.2, then × 100 = 20%. This is the formula behind test scores, completion rates, and "what proportion" questions.
Percentage change (increase or decrease)
To find how much something changed in percentage terms, take the new value minus the old value, divide by the old value, and multiply by 100. Going from 80 to 100: (100 − 80) ÷ 80 = 0.25, so a 25% increase. A negative result means a decrease.
- X% of Y = (X ÷ 100) × Y
- X is what % of Y = (X ÷ Y) × 100
- Percentage change = ((New − Old) ÷ Old) × 100
Percent off (discounts)
For a discount, multiply the price by the percent off to get the saving, then subtract — or multiply by what remains. A 25%-off item at 80: the price you pay is 80 × (1 − 0.25) = 80 × 0.75 = 60. Watch out for stacked discounts: "25% off plus an extra 10%" is applied one after another, not added, so it is less than 35% off.
🏷️Work out a sale priceDiscount Calculator →Reverse percentages
Sometimes you have the final amount and need the original — for example, a price that already includes tax. If a total of 120 includes 20% tax, divide by 1.20 to get the pre-tax price of 100. The rule: to remove an added percentage, divide by 1 plus that percentage as a decimal.
Every percentage question is one of these patterns. Spot which one you are facing, apply the matching step, and the arithmetic is easy.