Percentage Calculator
Calculate percentages instantly — find X% of Y, what percentage X is of Y, percentage change between two values, or add/subtract a percentage. Free.
What Is a Percentage Calculator?
Percentages come up constantly in everyday life — sale discounts, tax calculations, exam scores, interest rates, commission, survey results and statistical changes all involve percentages. The tricky part is knowing which formula to use for which question. This calculator covers all common scenarios with five modes: find a percentage of a number, find what percentage one number is of another, calculate percentage change, and apply percentage increases or decreases.
Percentage Formulas
| Mode | Formula | Example |
|---|---|---|
| X% of Y | Y × (X ÷ 100) | 15% of 80 = 12 |
| X is what % of Y | (X ÷ Y) × 100 | 45 is 75% of 60 |
| % change from A to B | ((B − A) ÷ |A|) × 100 | $50 to $65 = +30% |
| Increase N by X% | N × (1 + X ÷ 100) | $100 + 20% = $120 |
| Decrease N by X% | N × (1 − X ÷ 100) | $80 − 25% = $60 |
Real-World Use Cases
| Situation | Mode to Use |
|---|---|
| How much do I save on a 30% off sale? | X% of Y (then subtract from original) |
| Price after adding 20% VAT | Increase by % |
| I scored 42 out of 56 — what is my grade? | X is what % of Y |
| A share rose from $45 to $63 — by how much? | % change |
| My salary increased by 8% — new amount? | Increase by % |
Common Percentage Mistakes to Avoid
A frequent error is treating percentage changes as reversible. A 50% decrease followed by a 50% increase does not return to the original value — it leaves you at 75% of where you started. This is because the second operation applies to the new, smaller base. Always use the % change mode to compare a final value against its starting point rather than trying to "reverse" the original percentage.
Another common mistake is confusing percentage points with percentage change. If an interest rate rises from 2% to 3%, that is a 1 percentage-point increase but a 50% change in the rate itself. Financial reporting, political polling and medical studies all express these differently — use the X is what % of Y or % change modes to be precise about which type of comparison you mean.