Percentage Mental Math Tricks: Calculate Percentages in Your Head

The 10% Method

10% of any number is simply the number divided by 10 (move the decimal one place left). From there, you can calculate any multiple: 20% is 10% times 2, 5% is half of 10%, 15% is 10% + 5%, and so on. For a $48 bill, 10% is $4.80, so 15% tip is $4.80 + $2.40 = $7.20.

The 1% Trick

1% of any number is the number divided by 100 (move the decimal two places left). To find 7% of 80: 1% is 0.8, so 7% is 0.8 times 7 = 5.6. For a $250 item at 8% tax: 1% is $2.50, so 8% is $20.00.

The Double-and-Halve Method

To find a percentage where one number is easy to work with, double or halve both numbers. Finding 25% of 60? 25% is one quarter, and one quarter of 60 is 15. Finding 75% of 40? 75% is three quarters, and one quarter of 40 is 10, so three quarters is 30.