Most everyday percentages, like tips, discounts and price changes, can be worked out in a few seconds with a handful of tricks. Here are the five that cover almost everything.
1. Find 10% by moving the decimal point
To get 10% of any number, move the decimal point one place to the left. 10% of $84 is $8.40. 10% of 350 is 35. This is the building block for almost every other percentage.
- 20% = 10% doubled. 20% of $84 is $16.80.
- 5% = half of 10%. 5% of $84 is $4.20.
- 15% = 10% + 5%. 15% of $84 is $8.40 + $4.20 = $12.60.
- 30% = 10% × 3. 30% of $84 is $25.20.
2. Find 1% by moving it two places
Move the decimal point two places left to get 1%. 1% of $2,400 is $24, so 3% is $72 and 7% is $168. This is handy for sales tax and interest rates.
3. Flip it: X% of Y equals Y% of X
Percentages work in both directions. 8% of 50 is the same as 50% of 8, which is obviously 4. When one way looks hard, try the other: 4% of 75 is the same as 75% of 4, which is 3.
4. Use fractions for common percentages
| Percentage | Fraction | Example |
|---|---|---|
| 50% | ½ | 50% of 64 = 32 |
| 25% | ¼ | 25% of 64 = 16 |
| 75% | ¾ | 75% of 64 = 48 |
| 33⅓% | ⅓ | 33⅓% of 90 = 30 |
| 20% | ⅕ | 20% of 45 = 9 |
| 12.5% | ⅛ | 12.5% of 80 = 10 |
5. Percentage change: difference over the original
To find how much something went up or down in percent, divide the difference by the starting value. A price going from $40 to $50 rose by $10, and 10 ÷ 40 = 0.25, so that's a 25% increase.
Watch the direction: going back from $50 to $40 is a $10 drop on a $50 starting point, so it's only a 20% decrease. That's why a 50% loss needs a 100% gain to get back to where you started.
Putting it together: a discount example
A $129 jacket is 35% off. How much do you pay?
- 10% of $129 is about $13.
- 35% is 3½ times that: about $45.
- $129 − $45 = about $84.
The exact answer is $83.85, so the estimate is close enough to decide whether it's a good deal. When you need the precise number, the percentage calculator handles all four common percentage questions, and the tip calculator does tips and bill splitting.