Quick answer: A percentage is a fraction of 100: 25 percent means 25 out of 100. For changes, new value equals old times one plus or minus the percent over 100. Remember that percentage points differ from percent change: a rise from 10 to 12 percent is 2 points but 20 percent growth.
Last reviewed: September 2026
Key facts
- Three tools in one: X% of Y, X is what % of Y, and percentage change.
- A percentage is a fraction of 100 — 25% means 25 out of every 100.
- Percentage change = (new − old) ÷ |old| × 100.
- Percentage points and percent differ: 10% → 12% is +2 points but a 20% relative rise.
A percentage is simply a fraction of 100 — 25% means 25 out of every 100. This free percentage calculator answers the three questions people ask most: what is X% of Y, what percent X is of Y, and how much something changed in percent terms.
Choose the calculation, enter two numbers, and read the answer with a plain-English explanation underneath. It handles increases, decreases and values over 100% without breaking a sweat.
How to use
- Choose the calculation you need: “X% of Y”, “X is what % of Y” or “% change”.
- Enter X and Y in the two number fields.
- Read the result and the short explanation below it.
- Switch modes any time — your numbers stay put.
Percentage formulas
| Term | Meaning |
|---|---|
| X% of Y | The part: what you get when you take X percent of Y. |
| X is what % of Y | The share: X ÷ Y × 100. |
| Percentage change | Growth or shrink from old to new; negative means a decrease. |
For percentage change, dividing by the absolute old value keeps the sign meaningful: 80 → 60 is a 25% decrease.
Worked examples
The three modes
20% of 200 = 40. Choose “X% of Y”, enter 20 and 200.
30 is 15% of 200. Choose “X is what % of Y” — handy for working backwards from a part to the whole.
50 → 65 is a 30% increase; 80 → 60 is a 25% decrease. Choose “% change” and enter old then new.
Reverse percentage
90 is 75% of what? Divide the part by the decimal: 90 ÷ 0.75 = 120. This is the trick behind “was £120, now £90” sale labels.
Everyday percentage shortcuts
| Want | Do this | Of 240 |
|---|---|---|
| 10% | Divide by 10 | 24 |
| 20% | Divide by 5 | 48 |
| 25% | Divide by 4 | 60 |
| 50% | Halve it | 120 |
| 75% | Take 3/4 | 180 |
| 5% | Divide by 20 | 12 |
Combine shortcuts for anything else: 15% = 10% + 5%, so 15% of 240 = 24 + 12 = 36.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. From 50 to 65: (65 − 50) ÷ 50 × 100 = 30%.
Can a percentage be more than 100%?
Yes. 150% of 40 is 60. A value that doubles has grown by 100%; one that triples has grown by 200%.
What is the difference between percent and percentage points?
Percent is relative; points are absolute. A rate rising from 10% to 12% gains 2 percentage points, which is a 20% relative increase. Mixing them up is one of the most common statistics mistakes.
How do I reverse a percentage — find the whole from the part?
Divide the part by the percentage as a decimal. If 90 is 75% of the whole: 90 ÷ 0.75 = 120.
What is X% of Y if Y is zero?
Undefined in the “X is what % of Y” mode — you cannot divide by zero, so the calculator asks you to check the input.
How are discounts related to percentages?
A 25%-off sale means you pay 75% of the price. The Discount Calculator does the sale-price math for you.
Sources
- Khan Academy — Percentages and percent change
- Maths is Fun — Percentage calculations with examples
Key takeaways
- “X% of Y” finds the part; “X is what % of Y” finds the share; “% change” finds growth or shrink.
- Percentage points measure absolute moves, percent measures relative moves — don’t mix them.
- Reverse a percentage by dividing the part by the decimal form (90 ÷ 0.75 = 120).
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