Percentage Calculator
Calculate percentages, percentage of a value, and percentage change
Calculates percentages in three common directions — a percentage of a number, what percent one number is of another, and the percentage change between two numbers — with a mode switcher and labels that adjust to match.
How it works
Each mode is a distinct, simple formula: 'X% of Y' multiplies Y by X/100; 'X is what % of Y' divides X by Y and multiplies by 100; percentage change from X to Y computes (Y − X) / X × 100, shown with an up or down indicator depending on the sign. Switching modes clears both fields, since the same numbers rarely make sense across all three calculations.
Frequently asked questions
Why did switching modes clear my numbers?
The three modes ask fundamentally different questions, so a pair of values that made sense in one mode usually wouldn't mean the same thing in another — clearing avoids showing a result that looks valid but answers the wrong question.
Why did I get a division-by-zero error?
'What percent of Y' can't be computed if Y is zero, and percentage change can't be computed starting from zero (a change from zero is undefined as a percentage) — both are rejected with a clear error rather than showing Infinity or NaN.
What do the up/down arrows mean in percentage change mode?
An upward arrow and a '+' prefix mean the value increased from X to Y; a downward arrow with no prefix means it decreased. The color (accent for increase, red for decrease) reinforces the same signal at a glance.
Can I use negative numbers?
Yes — all three modes accept negative numbers where they make mathematical sense; only non-finite input (empty, non-numeric) and the specific division-by-zero cases are rejected.
Is my data sent anywhere?
No — every calculation is plain arithmetic that runs entirely in your browser. Nothing is uploaded.