Percentages turn up everywhere: exam marks, discounts, salary hikes, tax and interest. This percentage calculator has five modes for the most common questions, and each one shows the formula it used, so you can check the working or learn to do it by hand.
How to use the percentage calculator
- Choose one of the five modes (listed in the table below).
- Type the two numbers the mode asks for.
- Read the answer and the formula shown under it.
| Mode | Formula | Example |
|---|---|---|
| X% of Y | Y × X ÷ 100 | 15% of 2,400 = 360 |
| X is what % of Y | X ÷ Y × 100 | 432 out of 500 = 86.4% |
| % increase/decrease from A to B | (B − A) ÷ A × 100 | ₹40,000 to ₹46,000 = +15% |
| Add X% to Y | Y × (1 + X ÷ 100) | 1,200 + 8% = 1,296 |
| Subtract X% from Y | Y × (1 − X ÷ 100) | 2,999 − 20% = 2,399.20 |
What a percentage means
“Per cent” means “per hundred”. 18% is 18 out of every 100, or 0.18 as a decimal. Every mode in the calculator comes back to this idea: divide by 100 to turn a percentage into a decimal, and multiply by 100 to turn a fraction back into a percentage.
Percentage change: always divide by the starting value
For an increase or decrease, the starting value A is the base. If a salary goes from ₹40,000 to ₹46,000, the change is ₹6,000, and 6,000 ÷ 40,000 × 100 = 15%. A negative result means a decrease. A change from a starting value of 0 cannot be given as a percentage at all, because dividing by zero has no answer.
Watch out: A rise and a fall of the same percentage do not cancel out. If a price of ₹1,000 goes up 10% to ₹1,100 and then falls 10%, it ends at ₹990, not ₹1,000, because the second 10% is taken from a bigger number.
Percentage points versus per cent
If a loan rate moves from 8% to 9%, it has gone up by 1 percentage point, but by 12.5 per cent of the old rate (1 ÷ 8 × 100). News reports and bank letters sometimes mix these up, so check which one is meant.
Taking a percentage off a total that already includes it
Subtracting X% from Y is not the same as removing a tax that is already included in Y. If ₹1,180 includes 18% GST, the price before tax is 1,180 ÷ 1.18 = ₹1,000, not 1,180 − 18%. For that sum, use the “Remove GST” mode of the GST calculator.
If you want to see how percentage formulas look in code, the JavaScript operators lesson covers the arithmetic, and MDN’s guide to expressions and operators goes further.
Learn more
Frequently asked questions
How do I calculate my exam percentage?
Use the “X is what % of Y” mode: marks obtained as X and maximum marks as Y. 432 out of 500 is 86.4%. Some boards and universities use their own conversion rules, so check theirs for official use.
How do I find the original price before a discount?
Divide the sale price by (1 − discount ÷ 100). A ₹2,399.20 price after 20% off came from 2,399.20 ÷ 0.8 = ₹2,999.
Why does a 50% fall need a 100% rise to recover?
After a 50% fall, ₹100 becomes ₹50. To get back to ₹100, the ₹50 must double, which is a 100% increase on the new, smaller base.
How are results rounded?
Results are rounded for display. If you need a fixed number of decimal places, for example for money, round the final answer only, not the steps in between.