Percentage Calculator
The three percentage questions people actually ask, answered instantly. It runs entirely in your browser, so the file never leaves your computer.
Three questions, routinely confused
Nearly every percentage problem is one of three, and knowing which one you have is most of the work.
What is X% of Y — tips, discounts, sales tax, commission. X is what percent of Y — test scores, completion rates, share of a total. Percent change from X to Y — growth, price rises, anything measured twice.
Pick the mode and fill in the blanks. The modes exist because mixing them up is the actual error people make, not the arithmetic.
Why percent change is not symmetrical
This catches people constantly. Going from 80 to 100 is a 25% increase. Going from 100 back to 80 is a 20% decrease. Same two numbers, same gap, different percentages.
The reason is that a percentage is always relative to its starting point, and the two directions have different starting points. The tool states whether each result is an increase or a decrease so there is no ambiguity about which way you went.
Where it refuses to answer
Some percentage questions divide by one of your numbers, and dividing by zero is undefined — not a very large number, not zero, undefined.
If you enter zero where it cannot be used, you get told rather than shown a confident wrong answer. That is the right behaviour for a calculator, even though it looks less capable than one that just prints something.
Questions
Common questions
What does this tool do?
It answers the three percentage questions people search for most: what is X% of a number, what percentage one number is of another, and the percent change between two numbers. Pick a mode, fill in the blanks, and the answer appears instantly.
How do I find a percentage of a number?
Use the '% of a number' mode. For example, to find 15% of 200, enter 15 and 200 and you'll get 30. This is the one for tips, discounts, and sales tax.
How do I find what percent one number is of another?
Use the 'X is what % of Y' mode. For example, 30 out of 150 is 20%. Handy for test scores, completion rates, or any 'what share is this' question.
How do I calculate percent change?
Use the '% change' mode. Enter the starting and ending values — for example 80 to 100 is a 25% increase, and 100 to 80 is a 20% decrease. It tells you whether it's an increase or decrease.
Why can't it calculate with zero?
Some percentage questions divide by one of your numbers, and dividing by zero isn't defined. If you enter zero where it can't be used (the 'of' value, or the starting value for a change), the tool tells you instead of showing a wrong answer.
Is it private?
Yes. Everything is calculated in your browser — no ads, nothing uploaded.
Our own software
Dictate it instead of typing it
Hold a key, say the sentence, and the words land in whatever Windows window you were already in. Runs on your own PC — no account, no upload, nothing to renew.
$79 launch price · $99 regular · buy once