Percentage Calculator
What is X% of a number? What percent is A of B? Free and widely used.
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1. What is X% of a number?
What is % of ?
2. X is what percent of Y?
is what % of ?
3. Percent change between two values
From to
4. Increase or decrease a number by X%
by %
5. Find the original value (before a discount or tax)
Final price after a of %
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Quick demo: how to use this tool
- Choose the type of calculation (percentage of a number, discount, increase, etc.).
- Fill in the requested fields.
- Press calculate and copy the result if you need it.
How to calculate percentages: formulas and examples
This percentage calculator solves the five calculations people need most: what is X% of a number, X is what percent of Y, percent change between two values, increasing or decreasing a number by a percentage, and working backwards to the original value before a discount or sales tax. Results update as you type.
Percentage formulas
| What you want | Formula | Example |
|---|---|---|
| X% of Y | Y × X ÷ 100 | 20% of 150 = 150 × 20 ÷ 100 = 30 |
| X is what % of Y | X ÷ Y × 100 | 30 ÷ 120 × 100 = 25% |
| Percent change | (new − old) ÷ old × 100 | From 80 to 100: +25% |
| Increase by X% | Y × (1 + X ÷ 100) | 200 + 15% = 200 × 1.15 = 230 |
| Decrease by X% | Y × (1 − X ÷ 100) | 80 − 30% = 80 × 0.70 = 56 |
| Original before an increase | Final ÷ (1 + X ÷ 100) | $108 with 8% tax → 108 ÷ 1.08 = $100 |
| Original before a discount | Final ÷ (1 − X ÷ 100) | $56 after 30% off → 56 ÷ 0.70 = $80 |
Common mistakes
- Subtracting the percentage to remove tax. A $108 total with 8% sales tax does not equal $108 − 8% = $99.36. The tax was calculated on the pre-tax price, so divide by 1.08 to get $100.
- Assuming +20% then −20% returns to the start. $100 up 20% is $120, and $120 down 20% is $96.
- Adding discounts. 20% off and then 10% off is $100 × 0.80 × 0.90 = $72, a 28% total discount, not 30%.
- Mixing up percentage points and percent. Going from 10% to 12% is 2 percentage points but a 20% relative increase.
Everyday examples
| Situation | Calculation |
|---|---|
| 30% off an $80 jacket | $80 × 0.70 = $56 (you save $24) |
| 8% sales tax on $100 | $100 × 1.08 = $108 |
| 18% tip on a $45 meal | $45 × 0.18 = $8.10 |
| Test score: 36 right out of 40 | 36 ÷ 40 × 100 = 90% |
| Rent from $1,000 to $1,050 | (1,050 − 1,000) ÷ 1,000 × 100 = +5% |
For restaurant bills use the tip calculator, or see percentage change and growth for more detail.
How to use Percentage Calculator
- Open Percentage Calculator in RoviDev (you don't need to install anything or register).
- Enter the required data in the tool form.
- Press the button and see the result instantly on the screen.
Percentage calculator FAQ
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 20% of 150 is 150 × 20 ÷ 100 = 30.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. 30 out of 120 is 30 ÷ 120 × 100 = 25%.
How do I calculate percent change?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100 is +25%.
How do I take a discount off a price?
Multiply the price by (1 − discount ÷ 100). A $80 item at 30% off is 80 × 0.70 = $56.
How do I remove sales tax from a total?
Divide by 1 plus the tax rate. $108 at 8% tax is 108 ÷ 1.08 = $100 before tax.
Is a 20% increase followed by a 20% decrease back to the start?
No. $100 becomes $120 and then $96, because the second percentage applies to a larger base.
Related tools: Proportion calculator