To figure out 10 percent of any number, simply move the decimal point one place to the left. Ten percent of 250 is 25. Ten percent of 84 is 8.4. Ten percent of 7 is 0.7. That single trick works every time, no calculator needed.
The Decimal Point Shortcut
This is the fastest method and the one worth memorizing. Every number has a decimal point, even if you don’t see it written out. The number 300 is really 300.0, and the number 45 is really 45.0. To find 10 percent, slide that decimal point one spot to the left.
- 10% of 500 → move the decimal → 50.0 → 50
- 10% of 85 → move the decimal → 8.5
- 10% of 1,200 → move the decimal → 120.0 → 120
- 10% of 6.50 → move the decimal → 0.65
- 10% of 33 → move the decimal → 3.3
This works because dividing any number by 10 gives you exactly 10 percent of it. Moving the decimal point left is just a quick way to divide by 10 in your head.
The Multiplication Method
If you prefer a formula you can plug into a calculator or spreadsheet, multiply the number by 0.10. The decimal 0.10 is just another way of writing 10 percent. So the equation looks like this:
10% of a number = number × 0.10
For example, 10 percent of 50 is 0.10 × 50, which equals 5. Ten percent of 320 is 0.10 × 320, which equals 32. This formula is especially handy when you’re working in a spreadsheet. If your number is in cell A1, you’d type =A1*0.10 and the result appears instantly.
Using a Phone Calculator
On most smartphone calculators, you can use the percent button (%) to skip the decimal conversion entirely. Type the number, tap the multiplication sign, type 10, then tap the % button followed by equals. So for 10 percent of 450, you’d enter: 450 × 10 % =, and the screen shows 45.
If your calculator doesn’t have a percent button, just use the multiplication method: type 450 × 0.10 and hit equals. You get the same answer.
Real-Life Uses for 10 Percent
Knowing how to quickly find 10 percent is useful far more often than you might expect. Here are a few situations where it comes up regularly.
Tipping. Ten percent is the starting point for calculating tips at restaurants. If your bill is $72, ten percent is $7.20. Want to leave 20 percent? Just double that to $14.40. Want 15 percent? Add half of $7.20 (which is $3.60) to get $10.80.
Sale discounts. A store advertising 10 percent off makes the math easy. A $90 jacket at 10 percent off costs $90 minus $9, so you’d pay $81. For bigger discounts, you can stack tens: 30 percent off that jacket is three times $9, or $27 off, bringing the price to $63.
Savings goals. A common budgeting rule suggests saving 10 percent of your income. If you earn $4,000 a month, move the decimal and you know the target is $400.
Building Other Percentages From 10 Percent
Once you can find 10 percent in your head, you can quickly figure out almost any other percentage without a calculator.
- 5% — find 10%, then cut it in half. (5% of 200 = half of 20 = 10)
- 15% — find 10%, then add half of it. (15% of 80 = 8 + 4 = 12)
- 20% — find 10%, then double it. (20% of 150 = 15 × 2 = 30)
- 25% — find 10%, double it, then add half of 10%. (25% of 60 = 6 + 6 + 3 = 15)
- 1% — move the decimal two places left instead of one. (1% of 500 = 5)
By combining 10 percent and 1 percent, you can estimate virtually any percentage on the fly. Need 12 percent of 400? That’s 10 percent (40) plus two times 1 percent (4 + 4), giving you 48.