What is X% of Y?
Percentage change from Old to New
X is what percent of Y?
Add X% to a number
Subtract X% from a number
X is Y% of what number?
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“Note: This calculator provides estimated percentage calculations for everyday educational use. Please double-check all figures for official financial or academic purposes.”
How to Use This Percentage Calculator
Our calculator solves all three common percentage problems: finding a percentage of a number, finding what percentage one number is of another, and calculating percentage change between two values. Enter your numbers and get an instant answer with the full formula shown.
Type 1 – What is X% of Y?
Formula: Result = (X / 100) x Y
| Question | Answer |
|---|---|
| What is 20% of 500? | 100 |
| What is 15% of $80? | $12 |
| What is 8.5% of $1,200? | $102 |
| What is 30% of 250? | 75 |
Type 2 – X is What Percent of Y?
Formula: Percentage = (X / Y) x 100
| Question | Answer |
|---|---|
| 45 is what % of 180? | 25% |
| $30 is what % of $200? | 15% |
| 120 is what % of 400? | 30% |
Type 3 – Percentage Increase or Decrease
Formula: % Change = [(New – Old) / Old] x 100
| Scenario | Result |
|---|---|
| Price: $80 to $100 | +25% increase |
| Sales: 500 to 375 | -25% decrease |
| Salary: $60K to $66K | +10% increase |
| Weight: 200 to 185 lbs | -7.5% decrease |
Everyday Percentage Examples
- Shopping discounts: 30% off $150 = $45 savings, pay $105
- Restaurant tip: 18% on $65 bill = $11.70 tip
- Sales tax: 8.5% on $200 = $17 tax, total $217
- Salary raise: 5% raise on $55,000 = $2,750 more per year
- Investment return: 12% on $10,000 = $1,200 gain
Mental Math Shortcuts
| To Find | Shortcut |
|---|---|
| 10% | Move decimal one place left |
| 5% | Find 10%, then halve it |
| 25% | Divide by 4 |
| 20% tip | Find 10%, then double it |
| 1% | Move decimal two places left |
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Frequently Asked Questions
Multiply the number by the percentage, then divide by 100. For 15% of 80: 80 x 15 = 1,200, then 1,200 / 100 = 12. On most modern phones, you can type 80 x 15% and press equals directly.
If a rate goes from 2% to 3%, that is a 1 percentage point increase, but a 50% increase in the rate itself. Percentage points measure absolute change; percentage change measures relative change. This distinction matters greatly in finance and statistics.
Percent error = |Measured – True| / True x 100. If you estimated 45 but actual was 50: |45-50| / 50 x 100 = 10% error. Used in science and forecasting to measure accuracy.
To find the original value before a percentage increase: divide the result by (1 + rate). After 20% markup, price is $120: $120 / 1.20 = $100 original. After 15% discount, price is $85: $85 / 0.85 = $100 original.
It comes from Latin “per centum” meaning “per hundred.” So 25% means 25 out of every 100, or 0.25 as a decimal. Converting percentages to decimals always involves dividing by 100.