Percentage formulas used
- X% of Y = X ÷ 100 × Y. Example: 15% of 200 = 30.
- X is what % of Y = X ÷ Y × 100. Example: 30 is 15% of 200.
- Percentage change = (new − old) ÷ |old| × 100. From 50 to 75 is +50%; from 80 to 60 is −25%.
- Add a percentage = Y × (1 + X/100). ₹1,000 + 18% GST = ₹1,180.
- Remove a percentage = Y × (1 − X/100). A 20% discount on ₹2,500 leaves ₹2,000.
- Find the whole = part ÷ (X/100). If 30 is 15% of a number, the number is 200.
Common mistakes
Increase and decrease are not symmetric. A price that rises 20% and then falls 20% ends 4% lower than it started (100 → 120 → 96). Percent vs percentage points: an interest rate going from 8% to 10% is a rise of 2 percentage points, but a 25% increase in the rate. Removing tax already included: to get the price before 18% GST from ₹1,180, divide by 1.18 (= ₹1,000); do not subtract 18% (which gives ₹967.60).
Everyday uses
Marks to percentage (obtained ÷ total × 100), shop discounts, salary hikes, tips, credit card interest, investment returns, and price changes over time. Every row on this page works on its own, so you can keep several calculations on screen at once.
Tips
Use negative numbers when you need them, for example a percentage change from a loss. Results are rounded to six decimals. Your numbers stay on your device; nothing is uploaded.
FAQ
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 25% of 80 = 80 × 25 ÷ 100 = 20.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100.
How do I calculate marks percentage?
Divide marks obtained by total marks and multiply by 100. 450 out of 500 is 90%.
How do I remove GST from a price?
Divide the price including GST by (1 + rate/100). With 18% GST, divide by 1.18.
Why does +10% then −10% not return to the start?
The second percentage is taken from a bigger number. 100 + 10% = 110, and 110 − 10% = 99.