Percentage Calculator
Three common percentage calculations in one tool: find a percentage of a number, find what percent one number is of another, or find the percentage change between two numbers.
About the Percentage Calculator
"Percentage" questions come in three genuinely different shapes, and mixing them up is the most common source of percentage-math mistakes — this tool keeps them as three separate, clearly-labeled modes rather than one generic calculator that leaves you guessing which numbers go where.
The three modes, explained
X% of Y answers "what is 15% of 200?" — multiply Y by X/100. This is the mode for calculating a tip, a tax amount, or a portion of a total. X is what % of Y answers the reverse: "30 is what percent of 200?" — divide X by Y and multiply by 100. This is the mode for figuring out what share something represents (a test score out of total marks, a budget category's share of total spending). % change from X to Y answers "I went from 80 to 100 — what percent increase is that?" — subtract, divide by the original value, multiply by 100. This is the mode for price changes, growth rates, or any before-and-after comparison.
A common trap this avoids
A 20% increase followed by a 20% decrease does not return you to the original number — because the second 20% is calculated on the new, larger base. Using the "% change" mode twice (rather than assuming the changes cancel out) shows this directly.
Frequently Asked Questions
How do I find what percentage one number is of another?
Use the “X is what % of Y” mode — for example, to find what percent 30 is of 200, enter 30 and 200 to get 15%.
How is percentage increase or decrease calculated?
As the difference between the two numbers, divided by the original (starting) number, shown as a percentage — a positive result is an increase, negative is a decrease.