Percentage / Ratio Calculator

Choose a calculation type and enter values A and B to get the result instantly.

Calculation type

Enter values A and B.

About percentage calculations

Percentage math shows up constantly in everyday situations — figuring out a discount, calculating a tip, comparing two numbers, or working out how much something grew or shrank. This tool covers the four most common percentage calculations in one place: what percent A is of B, what value a percentage of A equals, the percentage change from A to B, and the value after increasing or decreasing A by a percentage.

The formulas behind each mode

"A is what % of B" computes (A ÷ B) × 100. "B% of A" computes A × (B ÷ 100). "Percentage change from A to B" computes ((B − A) ÷ A) × 100, giving a positive result for growth and negative for decline. "Value after changing A by B%" computes A × (1 + B ÷ 100), where a negative B% represents a decrease.

Frequently asked questions

What's the difference between a percentage point and a percentage change?
If a rate moves from 20% to 25%, that's a 5 percentage point increase, but a 25% relative increase (since 5 is 25% of the original 20). This tool's "percentage change" mode calculates the relative change, not the raw percentage-point difference.
Why do I get an error when B is 0?
Dividing by zero is mathematically undefined, so any mode that divides by your second value (like "A is what % of B" or percentage change starting from 0) can't produce a result when that value is 0 — you'll need a nonzero reference value.
Can percentage change be more than 100%?
Yes — if a value more than doubles, the percentage increase exceeds 100%. For example, going from 10 to 25 is a 150% increase, since the value grew by 1.5 times the original amount.