A percentage is a number out of 100. Here are the three calculations people need most often.
1. Find a percentage of a number
Formula: (Percentage / 100) x Number. Example: 15% of 80 = 0.15 x 80 = 12.
2. Find what percent one number is of another
Formula: (Part / Whole) x 100. Example: 30 is what percent of 120? 30 / 120 x 100 = 25%.
3. Find percentage change
Formula: ((New – Old) / Old) x 100.
- Increase from 50 to 65: (65 – 50) / 50 x 100 = 30% increase.
- Decrease from 80 to 60: (60 – 80) / 80 x 100 = 25% decrease.
Common mistakes
- Dividing by the new value instead of the old value when calculating change.
- Forgetting that a 50% increase followed by a 50% decrease does not return you to the original number.
Use our percentage calculator to check any of these quickly.
Try it now: Percentage Calculator