How this calculator works
X% of Y: divide X by 100 and multiply by Y. 15% of 80 is 0.15 × 80 = 12.
X is what percent of Y: divide X by Y and multiply by 100. 12 is 15% of 80.
Percent change from X to Y: (Y − X) ÷ |X| × 100. Going from 80 to 92 is a 15% increase.
Increase or decrease Y by X%: Y × (1 + X ÷ 100). Use a negative X for a decrease, such as −20 for a 20% discount.
Worked example
A price rising from $80 to $92
- Change: $92 − $80 = $12.
- Percent change: 12 ÷ 80 × 100 = 15%.
- Check: $80 increased by 15% = $80 × 1.15 = $92.
Questions people ask
Why doesn’t a 20% rise followed by a 20% fall get back to the start?
The fall is 20% of a larger number. 100 rises to 120, then 20% of 120 is 24, leaving 96.
What is the difference between percent and percentage points?
A rate going from 4% to 5% rises by 1 percentage point, which is a 25% increase in the rate itself.
How do I find the original price before a discount?
Divide the sale price by (1 − discount). A $60 price after 25% off was $60 ÷ 0.75 = $80.
Last reviewed October 2, 2026