The formulas
- P% of a number: number × P ÷ 100. For example, 15% of 240 = 240 × 15 ÷ 100 = 36.
- X is what percent of Y: X ÷ Y × 100. For example, 452 out of 500 = 452 ÷ 500 × 100 = 90.4%.
- Percentage change: (new − old) ÷ old × 100. From 50 to 65 is (65 − 50) ÷ 50 × 100 = 30%.
- Add or take off P%: number × (1 + P ÷ 100) or number × (1 − P ÷ 100).
- X is P% of what: X ÷ P × 100. If 36 is 15% of a number, the number is 36 ÷ 15 × 100 = 240.
Working out your marks percentage
Divide the marks you obtained by the total marks and multiply by 100. If you scored 935 out of 1,100, that is 935 ÷ 1,100 × 100 = 85%. Use the full total of every paper, including practicals, unless your board or university tells you to leave something out. Some universities convert a CGPA to a percentage with their own formula, so check their rule rather than using a general one.
The mistake most people make with tax and discounts
If a price of 1,180 already includes 18% tax, the price before tax is not 1,180 minus 18%. Taking 18% off 1,180 gives 967.60, which is wrong. The tax was added to the original price, so divide instead: 1,180 ÷ 1.18 = 1,000. In this calculator, use the “X is P% of what number?” card with 1,180 and 118 to get 1,000.
The same trap works in reverse. A price that rises 50% and then falls 50% does not return to where it started: 100 becomes 150, then 75.
Percent or percentage points?
When an interest rate moves from 10% to 12%, it has risen by 2 percentage points, but by 20 percent of its old value, because 2 is 20% of 10. News reports and bank offers mix these up, so check which one is meant. The “percentage increase or decrease” card gives the percent change.
Good to know
You can type numbers with commas, such as 1,00,000 or 1,000,000, and decimals such as 12.5. Results are rounded to 4 decimal places on screen. Every calculation happens in your browser.