Percentage Calculator
Five quick calculators in one for every everyday percentage question, from tips and discounts to growth rates and test scores.
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Percentages come up in more everyday situations than almost any other piece of math: shop discounts, restaurant tips, exam scores, pay rises, interest rates and statistics in the news. Each calls for a slightly different formula, and it is easy to mix them up. This page puts the five most common percentage calculations side by side. Fill in the boxes on any row and the answer appears instantly.
How to use the percentage calculator
Each row answers a different question. Find the one that matches yours, enter your numbers, and read the highlighted result. There is nothing to submit.
- What is X% of Y? For example, a 15% tip on an $80 bill.
- X is what % of Y? For example, scoring 12 out of 48.
- Percentage change from X to Y. For example, a price rising from $50 to $65.
- X is Y% of what? Finding the original total from a part.
- Increase or decrease X by Y%. For example, adding tax or taking off a discount.
The formulas
| Question | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 15% of 80 = 12 |
| X is what % of Y | X ÷ Y × 100 | 12 of 48 = 25% |
| % change | (new − old) ÷ old × 100 | 50 → 65 = +30% |
| X is Y% of what | X ÷ (Y ÷ 100) | 30 is 25% of 120 |
| Increase by Y% | X × (1 + Y ÷ 100) | 200 + 20% = 240 |
| Decrease by Y% | X × (1 − Y ÷ 100) | 200 − 20% = 160 |
Mental math tricks
- 10% is easy: move the decimal point one place left. 10% of 340 is 34.
- Build from 10%: 5% is half of 10%, 20% is double, and 15% is 10% plus 5%. So a 15% tip on $60 is $6 + $3 = $9.
- 1%: move the decimal point two places left, then multiply for any whole percentage.
- Swap the numbers: X% of Y always equals Y% of X. 8% of 50 is the same as 50% of 8, which is 4.
Mistakes to avoid
- Dividing by the wrong number in a percentage change. Always divide by the starting value. From 80 to 100 is a 25% increase, but from 100 to 80 is a 20% decrease.
- Adding percentages that apply in sequence. Two 10% discounts don’t make 20% off. They make 19% off, because the second applies to the already reduced price.
- Reversing a markup. To remove 20% sales tax from a total of $120, divide by 1.20 to get $100. Subtracting 20% would give $96, which is wrong.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 80 is 0.15 × 80 = 12.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 12 out of 48 is 12 ÷ 48 × 100 = 25%.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. Going from 50 to 65 is (65 − 50) ÷ 50 × 100 = 30% increase.
If a price rises 20% and then falls 20%, is it back where it started?
No. A 20% rise takes 100 to 120, and a 20% fall then takes 120 to 96. The fall is worked out on the larger number, so you end up 4% lower than you started.
What is the difference between percent and percentage points?
Percentage points measure the plain gap between two percentages, and percent measures the relative change. If an interest rate rises from 4% to 5%, that is 1 percentage point, but a 25% increase.