Percentage Calculator
Calculate percentages three ways: find a percentage of a number, work out what percentage one number is of another, or measure the increase or decrease between two values.
Formula and calculation
Worked example
To find 15% of 80: 80 × 15 ÷ 100 = 12. The calculator shows the same arithmetic as 80 × 15% = 12.
Percentage change is not symmetric
A 50% drop needs a 100% rise to get back to where it started: 100 → 50 is −50%, but 50 → 100 is +100%. That asymmetry is why investment losses are harder to recover from than they look, and it trips people up in reverse percentage problems all the time — “the price went down 20%, what do I add back?” is 25%, not 20% (divide by 0.8, don't multiply by 1.2). This calculator's third mode handles either direction exactly.
What the results mean
- Result
- The answer for the selected mode: the amount when finding X% of a number, a percentage when comparing X to Y, or the percent change from one value to another (positive means an increase, negative a decrease).
- Calculation
- The calculation written out with your numbers — so you can see exactly how the result was produced and reuse the method by hand.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 15% of 80 is 80 × 15 ÷ 100 = 12. The first mode here does this directly, including with percentages above 100% or negative values.
How do I find what percentage one number is of another?
Divide the first number by the second and multiply by 100. 30 out of 120 is 30 ÷ 120 × 100 = 25%. That is the second mode — useful for test scores, tips and budget shares.
How do I calculate percentage increase or decrease?
Subtract the old value from the new one, divide by the old value, and multiply by 100: (new − old) ÷ old × 100. Going from 80 to 100 is (100 − 80) ÷ 80 = +25%. The third mode labels the result as an increase or decrease for you.
Why is a 20% discount followed by a 20% increase not back to the original price?
Because the two percentages apply to different bases. $100 − 20% = $80, then $80 + 20% = $96, not $100. Percentages are compounding on the value they are applied to — that's also how compound interest works for you, and how fees work against you.