Use one calculator for common percentage questions, increases, decreases, and comparisons.
How to use the percentage calculator
Pick the type of question you want to answer from the tabs at the top, enter your two numbers, and press Calculate. The answer appears together with the formula used, so you can see exactly how it was worked out. The six modes cover almost every everyday percentage problem:
- What is X% of Y? – for tips, discounts, tax, and commissions
- X is what % of Y? – for test scores, budgets, and shares of a total
- Percentage change – how much something went up or down
- Increase by X% – a price after a raise or markup
- Decrease by X% – a price after a discount
- Percentage difference – how far apart two numbers are, when neither one is the starting point
The formulas, with examples
What is X% of Y?
Multiply Y by X and divide by 100. Example: 15% of 240 = 240 × 15 ÷ 100 = 36.
X is what % of Y?
Divide X by Y and multiply by 100. Example: you got 18 out of 72 questions right. 18 ÷ 72 × 100 = 25%.
Percentage change
Subtract the old value from the new value, divide by the old value, and multiply by 100. Example: rent goes from $800 to $920. (920 − 800) ÷ 800 × 100 = 15% increase. If the result is negative, it is a decrease.
Increase or decrease by X%
To increase, multiply by (1 + X ÷ 100). To decrease, multiply by (1 − X ÷ 100). Example: $50 increased by 12% is 50 × 1.12 = $56. A $120 coat at 25% off is 120 × 0.75 = $90.
Percentage difference
Take the difference between the two numbers, divide it by their average, and multiply by 100. Example: comparing 40 and 60, the difference is 20 and the average is 50, so the percentage difference is 40%. Use this when you are comparing two things side by side rather than measuring a change over time.
Common mistakes to avoid
- Percentage change is not symmetrical. A price that rises 50% and then falls 50% does not return to where it started. $100 becomes $150, then $75.
- Percent vs. percentage points. If an interest rate goes from 4% to 5%, it rose by 1 percentage point, but by 25% in relative terms. News reports often mix these up.
- Stacked discounts don’t add up. 20% off and then another 10% off is 28% off in total, not 30%, because the second discount applies to the already-reduced price.
Common questions
How do I calculate a percentage without a calculator?
Find 10% by moving the decimal point one place to the left, then build from there. 10% of 240 is 24, so 5% is 12 and 15% is 36.
What is the difference between percentage change and percentage difference?
Percentage change has a clear “before” and “after” and measures growth or decline. Percentage difference treats both numbers equally and is used for comparisons, such as the prices of the same item in two stores.
Related tools
- Tip Calculator – tips and bill splitting
- Compound Interest Calculator – see percentages grow over time
- Calculator – quick everyday arithmetic