A percentage calculator finds a percent of a number: multiply the number by the percent and divide by 100. For example, 15% of 80 = 80 × 15 ÷ 100 = 12.
The formulas below also answer what percent one number is of another, percent change, and increasing or decreasing by a percent.
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How to use the percentage calculator
- Enter the number, for example 80.
- Enter the percent, for example 15.
- Read the result: 12.
For a discount, the percentage calculator gives the amount off; subtract it from the price, or use the discount calculator for the sale price directly.
Percentage formulas
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Y × X ÷ 100 | 15% of 80 = 12 |
| X is what percent of Y? | X ÷ Y × 100 | 12 is 15% of 80 |
| X is P% of what? | X ÷ P × 100 | 12 is 15% of 80 |
| Percent change from A to B | (B − A) ÷ A × 100 | 80 to 92 = +15% |
| Increase Y by X% | Y × (1 + X ÷ 100) | 80 + 15% = 92 |
| Decrease Y by X% | Y × (1 − X ÷ 100) | 80 − 15% = 68 |
Percent of a number without a calculator
- 10%: move the decimal point one place left. 10% of 260 = 26.
- 5%: half of 10%. 5% of 260 = 13.
- 1%: move the decimal point two places left. 1% of 260 = 2.6.
- Build others: 15% = 10% + 5% = 39. 25% = a quarter = 65.
- Swap trick: X% of Y = Y% of X. 8% of 50 = 50% of 8 = 4.
Quick table
| Percent | of 50 | of 80 | of 200 | of 1,000 |
|---|---|---|---|---|
| 5% | 2.5 | 4 | 10 | 50 |
| 10% | 5 | 8 | 20 | 100 |
| 15% | 7.5 | 12 | 30 | 150 |
| 20% | 10 | 16 | 40 | 200 |
| 25% | 12.5 | 20 | 50 | 250 |
| 50% | 25 | 40 | 100 | 500 |
| 75% | 37.5 | 60 | 150 | 750 |
Percentages in Excel or Google Sheets
- X% of Y: =B1*A1 when A1 is formatted as a percent (15%), or =B1*A1/100 when A1 is a plain number (15).
- Percent change: =(B1-A1)/A1, formatted as a percent.
Common mistakes
- Percent vs percentage points: a rate going from 4% to 5% is a 1 percentage point rise but a 25% increase.
- Reversing a change: a 20% drop followed by a 20% rise does not get you back. 100 → 80 → 96.
- Wrong base: percent change always divides by the starting value.
Percent change examples
Percent change always divides by the starting value:
| From | To | Change | Percent change |
|---|---|---|---|
| 50 | 60 | +10 | +20% |
| 80 | 92 | +12 | +15% |
| 200 | 150 | −50 | −25% |
| 1200 | 1500 | +300 | +25% |
| 40 | 30 | −10 | −25% |
Notice that 50 to 60 is +20%, but 60 back to 50 is −16.67%: the base changes, so the percentages differ. The same trap appears with prices: a 25% markup followed by a 20% discount returns to the original price, because 1.25 × 0.80 = 1. To reverse a percent change, divide by the multiplier instead of subtracting the same percent: a price of 92 after a 15% rise was 92 ÷ 1.15 = 80.
Reverse percentages: finding the original number
A common question runs backwards: you know the result after a percentage was applied and want the starting figure. A shirt costs $34 after 15% off, so what was the full price? Subtracting 15% of $34 gives the wrong answer. The sale price is 85% of the original, so divide: $34 ÷ 0.85 = $40.
The same method works for increases. A salary of $57,750 after a 5% raise was $57,750 ÷ 1.05 = $55,000 before it. A bill of $64.20 that includes 7% sales tax had a pre-tax amount of $64.20 ÷ 1.07 = $60.00. In each case, turn the percentage into a multiplier, then divide by it.
A percentage calculator will not do this reversal unless you enter the multiplier yourself. You can check the answer with the percentage calculator: enter the original you found and the percent, and confirm it produces the amount you started with.
Shares of a total
Budgets and survey results often ask what share each part is of a whole. If monthly spending is $3,200 and rent is $1,150, the percentage calculator shows rent is 1,150 ÷ 3,200 × 100 = 35.9% of spending. Groceries at $520 are 16.3%. The shares should add up to 100%; if they come to 99.9% or 100.1%, that is just rounding. When you round each share, say so, so readers do not think something is missing.
Percentages of percentages
When one rate applies to part of another, multiply the rates. If 60% of customers are members and 25% of members renew, then 0.60 × 0.25 = 15% of all customers renew. Adding the percentages, 85%, has no meaning here. The percentage calculator handles one step at a time, so work through linked rates in order.
Related converters and calculators
Everyday uses:
- Discount calculator: sale prices
- Tip calculator: restaurant bills
- Sales tax calculator: tax on purchases
- Percent error calculator: measured vs true
- Ratio calculator: ratios
Sources
NIST SP 811, Chapter 7: expressing values, including percent.
Questions about this calculator
How do I calculate a percentage of a number?
Multiply the number by the percent 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 part by the whole and multiply by 100. 18 out of 24 is 75%.
How do I calculate percent increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. From 80 to 92 is 15%.
What is 10 percent of a number?
Move the decimal point one place to the left. 10% of 437 is 43.7.
What is the difference between percent and percentage points?
A rate going from 4% to 5% rises 1 percentage point, which is a 25% increase.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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