Three common percentage questions in one place: what is X% of Y, X is what percent of Y, and the percent change from one number to another.
The three formulas
| Question | Formula | Example |
|---|---|---|
| What is 20% of 150? | X ÷ 100 × Y | 30 |
| 30 is what % of 150? | X ÷ Y × 100 | 20% |
| % change from 50 to 65 | (Y − X) ÷ X × 100 | +30% |
Percentage points vs. percent
If a rate goes from 4% to 5%, it rose by 1 percentage point but by 25 percent. Mixing the two is one of the most common math mistakes in the news.
Frequently asked questions
How do I calculate a discount?
Use “What is X% of Y” to get the discount, then subtract it from the price. 25% off $80 is $20 off, so you pay $60.
Why is a 50% drop not undone by a 50% rise?
Percent change is measured from the starting value. $100 down 50% is $50; $50 up 50% is only $75.
How do I find the original price before a markup?
Divide by 1 plus the markup rate. A $120 price after a 20% markup started at $120 ÷ 1.2 = $100.
Related calculators
Results are rounded to four decimal places.
