Percentage Calculator
Type two numbers and the answer keeps pace with you, with the arithmetic jotted underneath like a note in the margin. Three percent questions, each with its own spot below.
Fill in both boxes and the answer lands here.
Good for test scores and "how much of the jar is left" moments.
Price went up? Went down? This tells you by how much.
How Percent Math Works
Percent just means "per hundred", so every percent problem is a divide-by-100 in disguise. To take 15% of 80, multiply 80 by 0.15 and you get 12. Going the other direction, 12 out of 80 is 12 divided by 80, which is 0.15, or 15%. Percent change compares the difference to where you started: from 50 to 75 is a jump of 25, and 25 divided by the original 50 is 0.5, a 50% increase.
The three formulas
X% of Y equals Y × (X ÷ 100). X as a percent of Y equals (X ÷ Y) × 100. Percent change from old to new equals (new - old) ÷ old × 100. That last one is the reason a drop from 80 to 60 is -25% but a climb from 60 back to 80 is +33%: the starting point changed.
Shortcuts worth keeping in your head
For a quick check at the register, 10% is just the decimal point moved one place left. Everything else builds from there.
| Shortcut | How | On $80 |
|---|---|---|
| 10% | move the decimal one place | $8.00 |
| 5% | half of 10% | $4.00 |
| 15% | 10% plus 5% | $12.00 |
| 20% | double 10% | $16.00 |
| 25% | divide by 4 | $20.00 |
| 50% | divide by 2 | $40.00 |
If you're comparing two quantities to each other rather than taking a slice of one, that's a job for the ratio calculator. And when the numbers arrive as fractions, the fraction calculator will turn 3/4 into 75% for you.