The three percentage questions everyone asks, in one place.
The three formulas
- A% of B = A ÷ 100 × B. Example: 15% of 80 = 12.
- A is what % of B = A ÷ B × 100. Example: 12 is 15% of 80.
- % change from A to B = (B − A) ÷ A × 100. Example: from 80 to 92 is a 15% increase.
Percentage points vs. percent
If an interest rate goes from 4% to 5%, it rose 1 percentage point, but 25 percent. Use the change mode with A = 4 and B = 5 to see it.
A common mistake
A 50% drop followed by a 50% rise does not get you back to the start: 100 → 50 → 75. Percent changes always apply to the current value.
Frequently asked questions
How do I calculate 20% of a number?
Multiply the number by 0.2. For 80, that is 16.
How do I find the percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100.
Can A or B be negative?
Yes, for percent of and percent change. Results with a negative starting value can be confusing, so double-check them.
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