What this percentage calculator does
This is four calculators in one. Pick a mode and fill in two numbers — the answer updates instantly:
- Percent of a value — what is 25% of 200?
- What percent — 50 is what percent of 200?
- Percentage change — how much did a value rise or fall from A to B?
- Increase / decrease — add or subtract a percentage from a value.
Everything is calculated locally in your browser.
The formulas behind it
| Question | Formula | Example |
|---|---|---|
| P% of N | N × P ÷ 100 | 25% of 200 = 50 |
| X is what % of Y | X ÷ Y × 100 | 50 of 200 = 25% |
| Change A → B | (B − A) ÷ A × 100 | 100 → 150 = +50% |
| N changed by P% | N × (1 + P ÷ 100) | 200 + 25% = 250 |
For increase/decrease, enter a negative percentage to subtract — for example −10% turns 200 into 180.
Where you will use it
- Shopping — a 30% discount off a price, or VAT added on top.
- Finance — interest, tips, growth from one figure to another.
- Work and study — test scores, conversion rates, year-on-year change.
- Everyday maths — splitting bills, comparing before-and-after numbers.
A note on percentage change
Percentage increase and decrease are not symmetric. If a price rises 50% and then falls 50%, you do not return to the start: 100 → 150 → 75. That is why the “percentage change” mode always measures relative to the starting value.
Privacy
The calculator runs entirely in your browser. Nothing is uploaded, and only your last mode and entries are stored locally so the tool opens where you left it.