How do I calculate a percentage?
Percentages exist solely so retail stores can pretend a $70 jacket was once worth $140. If you freeze every time someone asks what 18% of $64 is, you are in good company.
The short answer
To find X percent of a number, divide the percentage by 100 and multiply by the total. For example: 20% of 80 is 0.20 × 80 = 16.
Step 1: Turn the percentage into a decimal
Move the decimal point two spots to the left. 25% becomes 0.25. 7.5% becomes 0.075. 110% becomes 1.10.
Step 2: Multiply by your starting number
Take that decimal and multiply it by the amount you are measuring. If your restaurant bill is $45 and you want 20%, calculate 0.20 × 45 = 9.
Step 3: Add or subtract if calculating a change
For a discount, subtract that result from the original price. For sales tax or a tip, add that result to the original price.
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Common mistakes
- Forgetting that a 50% discount followed by another 50% discount equals 75% off, not free.
- Entering 5% as 0.5 instead of 0.05. 0.5 is 50%, which will ruin your calculation.
- Calculating percentage change by dividing by the new number instead of the starting number.