Free tool · runs in your browser
Percentage Calculator
Three calculators in one: a percentage of a number, a share of a total, and the change from one value to another.
The three formulas
- X% of Y —
X / 100 × Y. - X is what percent of Y —
X / Y × 100. - Change from X to Y —
(Y − X) / |X| × 100.
The tool evaluates all three from separate inputs, updates as you type, and lets you copy each result.
Percent versus percentage points
A change from 5% to 7% is an increase of 2 percentage points but a 40% relative increase. Both statements are correct; mixing them is one of the most common errors in reporting and pricing.
Use percentage points when comparing rates. Use percent change when comparing the size of the change relative to the starting value.
Change from zero and from negatives
Percent change from zero is undefined, because division by zero has no finite result; this calculator reports an error rather than inventing a number. With negative starting values, the denominator uses the absolute value, so a move from −100 to −50 shows +50%, meaning it moved halfway toward zero.
Frequently asked questions
Why does a change from -100 to -50 show +50%?
The denominator is the absolute starting value, so the move is measured relative to the distance from zero. Interpret the sign together with the direction of the values.
How do I calculate a discount?
If an item is 20% off, the price is 80% of the original: multiply by 0.8. Use the first calculator with X = 80 to get the sale price, or X = 20 for the amount removed.
Why is percent change from zero an error?
The formula divides by the starting value. When that value is zero, the result is undefined mathematically, so no honest percentage exists.
Can I use it for tips or tax?
Yes. A 15% tip on 80 is 0.15 × 80 = 12. Add the result to the original amount.
Is the calculation rounded?
Results are rounded for display. The copyable values are the displayed values, so use the formulas above if you need full precision.