10 percentage shortcuts you can do in your head
download.fan · Updated
Short answer
The core shortcut is 10%: move the decimal point one place left, so 10% of 240 is 24. Most other percentages build from it. Halve it for 5%, double it for 20%, and add 10% and 5% for 15%. Another useful trick is swapping the numbers, because x% of y always equals y% of x, so 8% of 25 is the same as 25% of 8, which is 2.
What are the 10 best percentage shortcuts?
- 10%: move the decimal one place left. 10% of 240 = 24.
- 1%: move the decimal two places left. 1% of 230 = 2.30.
- 5%: take 10% and halve it. 5% of 640 = 32.
- 50%: halve the number. 50% of 90 = 45.
- 25%: halve it twice. 25% of 48 = 12.
- 75%: take 25% and multiply by 3. 75% of 40 = 30.
- 20%: take 10% and double it. 20% of 85 = 17.
- 15%: take 10%, then add half of that. 15% of 80 = 8 + 4 = 12.
- Multiples of 1%: find 1% and multiply. 7% of 300 = 3 × 7 = 21.
- Swap the numbers: x% of y = y% of x. 8% of 25 = 25% of 8 = 2.
How do I work out a tip quickly?
Use the 15% or 20% shortcut. On a $62 bill, 10% is $6.20 and half of that is $3.10, so a 15% tip is $9.30. Double the $6.20 and a 20% tip is $12.40.
How do I work out a sale price in my head?
Find the discount and subtract it, or go straight to what you pay. At 20% off you pay 80%, so an $85 item costs $85 − $17 = $68. At 25% off you pay three-quarters, so a $40 item costs $30.
When should I use a calculator instead?
When the numbers don't divide neatly, or when the result matters. Mental math is great for estimating, while this percentage calculator gives exact answers on awkward figures like 17.5% of 1,284, and covers percentage differences and changes as well.