Find a percentage of a number, calculate percentage change, recover an original total, or increase and decrease a value. The selected operation determines which value is the reference total.
Part = total × rate / 100. Rate = part / total × 100. Change = (new − old) / old × 100. Original total = part × 100 / rate.
15% of 240 is 36. An increase from 80 to 100 is 25%. If 36 is 15% of the total, the total is 240. A price of 120 reduced by 25% becomes 90.
| Question | Calculation | Result |
|---|---|---|
| 15% of 240 | 240 × 15 / 100 | 36 |
| 80 rises to 100 | (100 − 80) / 80 × 100 | 25% increase |
| Original price after 20% off: 80 | 80 / (1 − 0.20) | 100 |
| A rate rises from 10% to 12% | 12 − 10; (12 − 10) / 10 × 100 | 2 percentage points; 20% relative increase |
Percentage points differ from percentage change: a rate rising from 10% to 12% rises by 2 percentage points but by 20% relative to its starting rate. Change from zero is undefined. A 20% fall followed by a 20% rise turns 100 into 96, not 100.
Divide the sale price by 1 minus the discount rate as a decimal. A sale price of 80 after 20% off came from 80 / 0.8 = 100. Simply adding 20% to 80 gives 96 and does not reverse the discount.
No. Change normally uses the old value as its reference. A symmetric percentage difference may use the mean of the two values instead. Choose the definition appropriate to the question; this calculator labels its starting-value change mode explicitly.
English edition: 16 September 2026.