How it works
Each mode uses its own formula:
- Percent of a number:
A% of B = A / 100 × B— e.g. 15% of 200 = 30 - Percent of a total:
A / B × 100— e.g. 30 of 200 = 15% - Percent change:
(New − Old) / Old × 100— e.g. 200 → 250 = +25%; 250 → 200 = −20%
Example
A price rises from $200 to $250: that's a +25% increase. If it then falls back to $200, that's only a −20% decrease — percentages are asymmetric because each applies to a different base. This is why a stock that drops 50% needs a 100% gain to break even.
What this calculator does not include
It handles plain percentage math on two numbers. It does not handle percentage-point differences (the difference between two percentages, e.g. 15% vs 20% is 5 percentage points, not 5%), compound growth, or tax-inclusive reverse calculations.
FAQ
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. For example, from 200 to 250: (250 − 200) / 200 × 100 = +25%.
Why do a 20% increase and a 20% decrease not cancel out?
Because each percentage applies to a different base. 100 + 20% = 120, but 120 − 20% = 96, not 100. The decrease is calculated on the larger number, so it removes more in absolute terms.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 200 is 30 / 200 × 100 = 15%.