One tool for every everyday percentage question. Pick the calculation, enter two numbers, and see the answer with the formula used.
Formulas
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | X ÷ 100 × Y | 15% of 240 = 36 |
| X is what % of Y? | X ÷ Y × 100 | 36 is 15% of 240 |
| % change from X to Y | (Y − X) ÷ X × 100 | 80 → 100 = +25% |
| Price after X% off | Y × (1 − X ÷ 100) | $60 with 25% off = $45 |
| Y plus X% | Y × (1 + X ÷ 100) | 200 + 18% = 236 |
Percentage change vs percentage points
If an interest rate goes from 5% to 6%, it rose by 1 percentage point but by 20 percent. Mixing these up is a common mistake in news reports.
Why a 50% drop needs a 100% rise to recover
Percentages are relative to the starting value. 100 falling 50% gives 50; getting from 50 back to 100 is a 100% increase. That’s why investment losses are harder to recover from than they look.
Mental math shortcuts
- X% of Y = Y% of X – so 8% of 25 is the same as 25% of 8 = 2.
- 10% → divide by 10; 5% → half of 10%; 1% → divide by 100.
- To add 18% GST or tax, multiply by 1.18.
Percentage change table
| From | To | Change |
|---|---|---|
| 50 | 60 | +20% |
| 60 | 50 | −16.67% |
| 80 | 100 | +25% |
| 100 | 80 | −20% |
| 200 | 300 | +50% |
| 300 | 200 | −33.33% |
Going up and coming back down are not symmetrical – which is why a 20% fall needs a 25% rise to recover.
Everyday percentage problems
- Discounts: a $80 jacket at 30% off costs $80 × 0.7 = $56.
- Stacked discounts: 20% off then an extra 10% off is not 30% off – it’s 1 − (0.8 × 0.9) = 28% off.
- Sales tax: $45 plus 8.25% tax = $45 × 1.0825 = $48.71.
- Exam marks: 47 out of 60 = 47 ÷ 60 × 100 = 78.33%.
- Salary hikes: see the salary hike calculator.
- Interest: 5% a year on 2,000 is 100 a year (simple interest).
Reverse percentages
If a price after a 25% discount is 60, the original price was 60 ÷ 0.75 = 80 – not 60 × 1.25 = 75. Reverse percentages always divide by the multiplier that was applied.
Percentage difference vs percentage change
Percentage change compares a new value to an old one. Percentage difference compares two values with no natural “before” and “after”, using their average: |A − B| ÷ ((A + B) ÷ 2) × 100. For 40 and 60 that’s 20 ÷ 50 × 100 = 40%.
Converting fractions and decimals
To turn a fraction into a percentage, divide and multiply by 100: 3/8 = 0.375 = 37.5%. To turn a percentage into a decimal, divide by 100: 12.5% = 0.125.
Real-life scenarios
- Black Friday deals: A $249 TV at 35% off costs $161.85 – you save $87.15.
- Exam results: 412 marks out of 500 is 82.4%.
- Investments: A stock bought at $40 and now at $46 is up 15%.
- Restaurant bill: 18% of $64 is $11.52.
- Business growth: Sales rose from ₹8 lakh to ₹10 lakh – a 25% increase.
- Price increases: Rent going from $1,500 to $1,575 is a 5% rise.
Percentages in finance
Interest rates, inflation, returns and taxes are all percentages – but they compound. A 7% annual return doesn’t add 70% over ten years; it nearly doubles your money (1.07¹⁰ ≈ 1.97). For compounding calculations, try the FD calculator or SIP calculator.
Related calculators
- GST / VAT calculator – add or remove sales tax
- Salary hike calculator – raises and hike %
- Tip calculator – tips and bill splits
FAQs
How do I calculate 20% of a number?
Multiply by 0.2, or divide by 5. 20% of 350 is 70.
What is the formula for percentage increase?
(New − Old) ÷ Old × 100. From 120 to 150: 30 ÷ 120 × 100 = 25%.
How do I calculate a percentage of marks?
Use “X is what % of Y” with your marks as X and the total as Y. 412 out of 500 is 82.4%.
How do I reverse a percentage?
To find the original price before a 20% increase, divide by 1.2. For GST, use the GST calculator.