How to use the percentage calculator
- Pick the calculation you need from the three buttons at the top.
- Fill in the two values — the labels change to match the mode you chose.
- Press "Calculate" and read the answer below the inputs.
- Switch modes at any time and the result updates to the new calculation.
The three calculations explained
Percentages show up everywhere: discounts, tips, taxes, exam scores, interest rates and growth figures. This tool covers the three sums people reach for most often, each with a simple formula.
| Mode | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 15% of 250 = 37.5 |
| X is what % of Y | X ÷ Y × 100 | 15 is 6% of 250 |
| % change from A to B | (B − A) ÷ A × 100 | From 200 to 250 is +25% |
Reading a percentage change
The change mode measures how much a value has moved relative to where it started. A positive result means an increase, and a negative result means a decrease. This is the calculation behind "sales are up 12% this quarter" or "the price dropped 8%". Because it divides by the starting value, the starting value must be greater than zero for the answer to be meaningful.
Common uses
Shoppers use the first mode to work out how much they will save in a sale. Students use the second mode to convert a test score into a percentage. Business owners use the third mode to track revenue, traffic or cost changes from one period to the next. Whatever the use case, the answer is instant and nothing you type leaves your browser.
Tips for avoiding percentage mistakes
The most common error is forgetting to convert the percentage to a decimal. Remember that "percent" means "per hundred", so 15% is 15 ÷ 100, or 0.15. Another common slip is mixing up which number is the whole when asking "X is what percent of Y" — the value after the word "of" is the whole. When measuring change, always divide by the original starting value, not the new one, or the result will be off.