Percentage Calculator
Calculate percentages three ways: X% of Y, what percent X is of Y, and percentage change.
Percentage questions come in more than one shape, and it's easy to grab the wrong formula under time pressure — finding what 15% of a restaurant bill is, figuring out what percentage a test score represents, or calculating how much a value grew or shrank between two points in time are three genuinely different calculations that all get lumped together as "percentage math."
This calculator covers the three most common cases as separate tabs: X% of Y (multiply Y by the percentage), what percent is X of Y (divide X by Y and convert to a percentage), and percentage change between two values (the difference divided by the original value). Each tab updates its result instantly as you type, so you can jump between calculation types without re-deriving the formula each time.
Percentage change in particular trips people up because the direction matters — going from 100 to 150 is a 50% increase, but going from 150 back to 100 is only a 33.3% decrease, not 50%, since percentage change is always relative to the starting value.
How to use Percentage Calculator
- 1
Pick the calculation type
Choose the tab matching your question: X% of Y, what percent, or percentage change.
- 2
Enter your numbers
Fill in the two relevant values for that calculation type.
- 3
Read the result
The answer updates instantly as you type.
Features
- Covers the three most common percentage calculation types
- Instant live results with no button press needed
- Clearly labels increases vs. decreases
- Works with decimals and negative numbers
Frequently asked questions
Common mistakes to avoid
- Assuming a percentage increase and the equivalent percentage decrease cancel each other out — they don't, since the base value changes.
- Confusing 'percent of' with 'percentage points' when comparing two percentages (e.g., going from 20% to 25% is a 5 percentage point increase, but a 25% relative increase).
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