X% of Y, percent of a total, increase, decrease, and difference — all in one tool.
Percentage problems come in several genuinely different shapes — finding what X% of a number is, working out what percent one number is of another, or measuring how much something has grown or shrunk — and each needs a different calculation. Rather than making you remember which formula applies, this tool offers five explicit modes (X% of Y, X is what % of Y, % Increase, % Decrease, and % Difference), shows the formula it used, and gives the result instantly as you type.
Choose a mode — X% of Y, X is what % of Y, % Increase, % Decrease, or % Difference — enter your two values, then tap Calculate to see the formula and result.
Percentages are always relative to a starting value. Going from 80 to 100 is +25% because the base is 80, but going back from 100 to 80 is −20% because the base is now 100. This is why a 50% increase followed by a 50% decrease leaves you below where you started: 100 becomes 150, then 75. Keep this in mind when comparing investment returns, price changes and growth figures.
Make sure you identify the "original" value correctly in increase and decrease problems, because swapping the two numbers changes the answer. When the original value is zero, percentage change is undefined, so the tool cannot give a meaningful figure. For shopping maths, the Discount Calculator gives the final price and savings directly, and the GST / VAT Calculator handles tax. Our guide on how to calculate any discount or sale price walks through the same formulas by hand.
What's the difference between % Increase and % Difference?
% Increase/Decrease measures change relative to the original value; % Difference measures the gap relative to the average of both values, useful when there's no clear "original".
Can I use negative numbers?
Yes, though results in Increase/Decrease mode are most meaningful when the original value isn't zero.
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