Percentage Calculator
One tool for every percent question: what is X% of Y, the percentage increase or decrease between two numbers, adding or subtracting a percent, and reverse percentage to find the original price before a discount or markup.
How to use this percentage calculator
Percentages come up everywhere — exam scores, discounts, tips, tax, interest, statistics and price changes. Instead of hunting for a different tool each time, this single percentage calculator covers the seven most common questions. Pick the calculation type from the dropdown and the two input labels update to match, so you always know exactly what to type.
Here are the formulas behind each mode:
What is X% of Y = Y × X ÷ 100
X is what % of Y = X ÷ Y × 100
% change = (new − old) ÷ old × 100
Add X% = Y × (1 + X ÷ 100) • Subtract X% = Y × (1 − X ÷ 100)
Reverse markup = price ÷ (1 + X ÷ 100) • Reverse discount = price ÷ (1 − X ÷ 100)
Worked examples
Percent of a number: 20% of 150 = 150 × 20 ÷ 100 = 30. Percentage change: a price rising from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase; falling from 100 to 80 is a 20% decrease. Reverse discount: if a jacket costs 80 after a 20% sale, the original price was 80 ÷ 0.80 = 100 — a common question that trips people up because 80 + 20% is not 100.
Percentage quick-reference
| You want to… | Do this | Example |
|---|---|---|
| Find a percent of a number | × percent ÷ 100 | 15% of 200 = 30 |
| Turn a fraction into a percent | part ÷ whole × 100 | 45/60 = 75% |
| Measure growth | (new − old) ÷ old × 100 | 80→100 = +25% |
| Add tax or a tip | × (1 + percent ÷ 100) | +18% on 50 = 59 |
| Undo a discount | ÷ (1 − percent ÷ 100) | 80 after −20% = 100 |
Percentages are ratios out of 100 — “per cent” literally means “per hundred.”
Frequently asked questions
How do I calculate what is X percent of Y?
Multiply the number by the percent and divide by 100. 20% of 150 = 150 × 20 ÷ 100 = 30.
How do I calculate percentage increase or decrease?
Percentage change = (new − old) ÷ old × 100. From 80 to 100 is +25%. A negative result is a decrease.
What is a reverse percentage calculation?
It finds the original amount before a percent was added or removed. 120 after a 20% markup came from 120 ÷ 1.20 = 100; 80 after a 20% discount came from 80 ÷ 0.80 = 100.
How do I add or subtract a percentage from a number?
Add: × (1 + percent ÷ 100). Subtract: × (1 − percent ÷ 100). 200 + 15% = 230; 200 − 15% = 170.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. 45 out of 60 = 75%.
What's the difference between percentage change and percentage difference?
Change is relative to the old value; difference is relative to the average of both values and is always positive.