Three percentage calculators in one
Percentages are everywhere: discounts, tax, tips, exam marks, business growth and price rises. This percentage calculator handles the three questions people ask most often, and the answers update instantly as you type.
1. What is X% of Y?
Use this for discounts, tax and tips. Formula: (X ÷ 100) × Y. Example: 20% of 150 = 30, so an item priced at 150 with 20% off costs 120.
2. X is what percent of Y?
Use this for exam scores, targets and shares of a total. Formula: (X ÷ Y) × 100. Example: 30 out of 120 = 25%.
3. Percentage increase or decrease
Use this to compare prices, sales, traffic or any value over time. Formula: ((New − Old) ÷ Old) × 100. Example: from 80 to 100 is a 25% increase, and from 100 to 80 is a 20% decrease.
Common mistakes
- A 50% increase followed by a 50% decrease does not bring you back to the start: 100 → 150 → 75.
- Percentage change uses the old value as the base, not the new one.
- Percentage points differ from percent: a rate going from 5% to 6% is a 1 percentage point rise, but a 20% increase.
Need to work out an exact age instead? Use the age calculator.
Everyday percentage examples
- Discount: 25% off a price of 80 = 80 × 0.25 = 20 off, so you pay 60.
- Tip: a 15% tip on a bill of 46 = 6.90.
- Tax: adding 20% VAT to 150 = 150 × 1.2 = 180.
- Exam score: 42 out of 60 = (42 ÷ 60) × 100 = 70%.
- Growth: website visits rising from 2,000 to 2,600 = a 30% increase.
Reverse percentages
If a price after 20% tax is 180, the price before tax is 180 ÷ 1.2 = 150, not 180 − 20% (which gives 144). To reverse a percentage increase, divide by (1 + rate). To reverse a discount, divide by (1 − rate).
Percentage change vs. percentage points
If an interest rate goes from 4% to 5%, it has risen by 1 percentage point, but by 25 percent relative to where it started. News reports and business dashboards often mix these up, so check which one is meant.
Quick mental maths tricks
- 10% of a number: move the decimal point one place left (10% of 340 = 34).
- 5%: half of 10% (17).
- 1%: move the decimal two places (3.4).
- X% of Y equals Y% of X, so 8% of 50 is the same as 50% of 8 = 4.
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 200 = 0.15 × 200 = 30.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100.
Can I use decimals and negative numbers?
Yes. All three calculators accept decimals and negative numbers.
How do I work out a discount price?
Use the first calculator to find the discount amount, then subtract it from the original price.