Six ways to calculate percentages — results update instantly
Every percentage calculation comes down to three variables: the part, the whole, and the percentage. Know any two and you can find the third.
The word "percent" means "per hundred" — it's a ratio expressed as a fraction of 100. So 25% simply means 25 out of every 100, or 0.25 as a decimal. To find 25% of any number, multiply it by 0.25.
Quick reference for common percentages of round numbers — useful for mental math and sanity-checking calculator results.
| Percentage | Of 100 | Of 200 | Of 500 | Of 1,000 |
|---|---|---|---|---|
| 5% | 5 | 10 | 25 | 50 |
| 10% | 10 | 20 | 50 | 100 |
| 15% | 15 | 30 | 75 | 150 |
| 20% | 20 | 40 | 100 | 200 |
| 25% | 25 | 50 | 125 | 250 |
| 33% | 33 | 66 | 165 | 330 |
| 50% | 50 | 100 | 250 | 500 |
| 75% | 75 | 150 | 375 | 750 |
One of the most misunderstood things about percentages is that a percentage increase and the equivalent percentage decrease are not the same number. If a price rises 50% and then falls 50%, you do not end up back where you started.
Example: a $100 item rises 50% to $150. A 50% decrease from $150 brings it to $75 — not $100. That's because the second percentage is calculated on the new, larger base.
This asymmetry matters in investment discussions ("the market is up 100% — it just needs to fall 50% to break even"), salary negotiations, and any situation where a number goes up and then comes back down.
To reverse a percentage increase exactly, use the formula: reverse % = (increase% ÷ (1 + increase%)) × 100. A 25% increase requires a 20% decrease to return to the original value.
This percentage calculator offers six calculators in one page: finding X% of Y, finding what percentage one number is of another, calculating percentage change between two values, increasing or decreasing a value by a percentage, and splitting a bill with tip. All results update instantly as you type. Nothing is sent to any server.