How to use the Percentage Calculator
- Find the calculator that matches your question — e.g. What is X% of Y? for a tip or Percentage change for growth.
- Type your numbers into the fields. Decimals and negative numbers work.
- The result updates instantly, with the formula shown underneath so you can verify the calculation.
- Click Copy to copy a result.
What is a percentage?
“Per cent” means “per hundred”: 25% is 25 out of 100, or the fraction 0.25. Percentages make it easy to compare quantities of different sizes — a discount, an interest rate, a conversion rate or a change in traffic. Every calculation on this page is a variation of one relationship: part = percent ÷ 100 × whole.
Percentage formulas with examples
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | X ÷ 100 × Y | 15% of 200 = 30 |
| X is what % of Y? | X ÷ Y × 100 | 45 of 180 = 25% |
| % change from X to Y | (Y − X) ÷ |X| × 100 | 80 → 100 = +25% |
| Increase Y by X% | Y × (1 + X ÷ 100) | 50 + 20% = 60 |
| Decrease Y by X% | Y × (1 − X ÷ 100) | 50 − 20% = 40 |
| Original before X% increase | Y ÷ (1 + X ÷ 100) | 120 after +20% → 100 |
| X is P% of what? | X ÷ (P ÷ 100) | 30 is 15% of 200 |
| % difference | |X − Y| ÷ ((X + Y) ÷ 2) × 100 | 40 vs 60 = 40% |
Percentage change vs percentage difference
Percentage change has a direction: it compares a new value to an old one, so going from 80 to 100 is +25%, but going from 100 to 80 is −20%. Percentage difference compares two values without a “before” and “after” by dividing by their average, so 40 vs 60 and 60 vs 40 both give 40%. Use change for growth over time, difference for comparing two products or measurements.
Common percentage mistakes
- Reversing a discount: a price that rose 20% doesn’t return to the original after a 20% cut — 100 → 120 → 96. To undo a 20% increase, divide by 1.2 (that’s what the reverse calculator does).
- Removing VAT or sales tax: to get the net price from a gross price including 19% VAT, divide by 1.19 — don’t subtract 19%. 119 ÷ 1.19 = 100, while 119 − 19% = 96.39.
- Percent vs percentage points: a conversion rate moving from 2% to 3% is a rise of 1 percentage point, but a 50% relative increase.
- Stacking changes: +10% then +10% is +21% overall (1.1 × 1.1 = 1.21), not +20%.
Working with ratios rather than percentages? Try the Aspect Ratio Calculator, or convert between measurement systems with the Unit Converter.
Tools that pair well with the Percentage Calculator
- Date Difference Calculator — Count the days between two dates — including business days and a years/months/days breakdown — add or subtract time from a date, or run a live countdown.
- Number Base Converter — Type a number in any base and see it in all the others instantly.
- Time Zone Converter — Convert any time between cities and time zones, see the current time everywhere, and find a meeting slot that falls in everyone’s working hours.