Percentage formulas
| Question | Formula | Example |
|---|---|---|
| X% of Y | X × Y ÷ 100 | 15% of 240 = 36 |
| X is what % of Y | X ÷ Y × 100 | 45 is 25% of 180 |
| % change | (Y − X) ÷ X × 100 | 1,250 → 1,400 = +12% |
Percent vs. percentage points
If a rate rises from 4% to 5%, it went up by one percentage point, but by 25% in relative terms. News reports about interest rates and polls usually mean percentage points.
Frequently asked questions
Is a 50% increase undone by a 50% decrease?
No. 100 increased by 50% is 150, and 150 decreased by 50% is 75. The second change applies to a larger starting number.
How do I add a percentage to a number?
Multiply by 1 plus the percentage as a decimal. Adding 8% to 250 is 250 × 1.08 = 270.