Percentage Calculator: Every Percent Problem in One Place
A percentage is a fraction of one hundred, and almost every percentage question is one of three types: what is X% of Y, X is what percent of Y, and what is the percentage change from X to Y. This calculator handles all three, which covers discounts, tips, tax, grades, interest and statistics.
The three core operations
- Percentage of a number: multiply by the percent and divide by 100. 15% of 240 = 36.
- One number as a percent of another: divide, then multiply by 100. 36 of 240 = 15%.
- Percentage change: (new − old) ÷ old × 100. From 240 to 300 is a 25% increase.
Increases and decreases do not cancel
A 20% rise followed by a 20% fall does not return you to the start. 100 rises to 120, then falls to 96. This is why a stock that drops 50% needs a 100% gain to recover, and why sequential discounts stack multiplicatively rather than by addition — 20% off then a further 10% off is 28% off, not 30%.
Percent versus percentage point
If a rate moves from 4% to 6%, it has risen by two percentage points but by 50 percent. Mixing these up is one of the most common errors in reporting on interest rates, polling and conversion metrics. Use percentage points when comparing two percentages and percent when describing relative change.
Quick mental shortcuts
- 10% is the number with the decimal point moved one place left.
- 5% is half of 10%; 20% is double it; 15% is 10% plus 5%.
- X% of Y always equals Y% of X — 8% of 50 is the same as 50% of 8, which is 4.
Key takeaways — Percentage Calculator
- Learn the three forms and every percentage question becomes routine.
- Percentage changes compound; they never simply add or cancel.
- Percent and percentage point mean different things — say which you mean.