What is X% of Y?
% of
=
50
X is what percent of Y?
is
25%
of
Percentage Change
Percent Change
Change
+25%
Direction
📈 Increase
Absolute Diff
+20
Increase / Decrease a Value by X%
Result
Result
600
Change Amount
+100
X is Y% of what number?
is
% of
150
The five calculators on this page
Each box answers one common question and updates as you type: what is X% of Y, X is what percent of Y, the percentage change from one value to another, a value increased or decreased by X%, and the whole when you know that X is Y% of it. Nothing you type leaves your browser.
Formulas and examples
| Question | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 20% of 250 = 50 |
| X is what % of Y | X ÷ Y × 100 | 50 ÷ 200 × 100 = 25% |
| % change from A to B | (B − A) ÷ |A| × 100 | (100 − 80) ÷ 80 × 100 = +25% |
| Y increased by X% | Y × (1 + X ÷ 100) | 500 × 1.20 = 600 |
| Y decreased by X% | Y × (1 − X ÷ 100) | 500 × 0.80 = 400 |
| X is Y% of what | X ÷ (Y ÷ 100) | 45 ÷ 0.30 = 150 |
Mistakes that catch people out
- Up then down is not back to the start. A price of 500 raised 20% is 600. Cut that 20% and you get 480, not 500, because the 20% is now taken from a bigger number. The change from 100 to 80 is −20%, but getting from 80 back to 100 takes +25%.
- Two discounts do not add up. 20% off followed by another 10% off is 200 → 160 → 144, so 28% off in total, not 30%.
- Percent versus percentage points. If an interest rate moves from 4% to 5%, it rose by 1 percentage point, which is a 25% increase. News stories mix these up constantly.
- Markup is not margin. An item that costs 80 and sells for 100 has a 25% markup (20 ÷ 80) but a 20% margin (20 ÷ 100). Using one when you mean the other misprices things.
- The base matters. "X is what percent of Y" divides by Y, the thing you are comparing against. Swapping the two gives a different answer: 50 is 25% of 200, but 200 is 400% of 50.
- Change from zero is undefined. Going from 0 to 10 cannot be expressed as a percentage change, so the calculator shows a dash. For a negative starting value it divides by the absolute value, so the sign shows the direction of the change.
Everyday uses
- Discount and tax. 15% off 240 is 240 × 0.85 = 204. Adding 5% sales tax gives 204 × 1.05 = 214.20. The order does not matter here, since multiplying is commutative: tax first and then the discount also gives 214.20.
- Year-on-year change. Revenue of 80 last year and 100 this year is +25%.
- Working back to the original. If a 30% deposit is 45, the full price is 45 ÷ 0.30 = 150.
For tips and tax on a bill, the tip calculator and sales tax calculator do the sums for you.
Frequently Asked Questions
To find X% of Y: multiply Y by X, then divide by 100. Example: 20% of 150 = (150 × 20) ÷ 100 = 30. Or simply move the decimal: 20% of 150 = 0.20 × 150 = 30.
Percentage change = ((New − Old) ÷ Old) × 100. A positive result is an increase, negative is a decrease. Example: price rises from $80 to $100 → ((100−80) ÷ 80) × 100 = +25%.
Percentage points are an absolute difference between two percentages. If interest rates rise from 3% to 5%, that's a 2 percentage point increase — but a 66.7% relative increase, since (5-3)/3 × 100 = 66.7%. The two terms are often confused in financial news.