Six common percentage problems in one tool: find a percentage of a number, what percent one number is of another, percent change, add or subtract a percentage, find the original number, or the percentage difference between two values.
15% of 200 is 30.
A percentage is a number expressed out of 100. This calculator handles six common problems, and each one uses a short formula:
Percentage of a number: 15% of 200 is (15 ÷ 100) × 200 = 30. Other quick ones: 10% of 85 is 8.5, 20% of 50 is 10, 25% of 80 is 20, and 5% of 1,200 is 60.
What percent one number is of another: 30 out of 200 is (30 ÷ 200) × 100 = 15%. On a test, 42 correct out of 50 is 84%, and 18 out of 24 is 75%.
Percent change: going from 200 to 230 is a change of 30, so (30 ÷ 200) × 100 = a 15% increase. Going the other direction, from 230 back down to 200, is a change of −30 on a base of 230, which works out to roughly a 13% decrease. It is not the same 15%, since percent change is always relative to the starting number. A town that grows from 12,500 to 13,150 people grew by 5.2%, and a price that falls from $4.50 to $3.60 dropped by 20%.
You can estimate many percentages in your head. Move the decimal point one place left to find 10%. For 84, 10% is 8.4. Half of that gives 5%, which is 4.2. Add the two to get 15%, which is 12.6. Double the 10% figure for 20%. And 1% is two places to the left, so 1% of 84 is 0.84.
Percentages often show up next to unit changes, such as a price per pound versus per kilogram; the unit and currency converter handles those. For restaurant bills, the tip calculator works out the tip and splits the total between people.
What's the difference between percentage points and percent change?
If a rate moves from 20% to 25%, that's a 5 percentage point increase, but a 25% relative increase in the rate itself. This calculator's "% change" mode gives the relative change.
Can I use negative numbers?
Yes, the percent change calculation works with negative starting or ending values, though results can be harder to interpret in those cases.
How do I calculate a discount using this tool?
Use "Add or subtract %" and choose subtract. Enter the original price and the discount percentage, and the result is the sale price, with the amount saved shown below it. For example, 20% off $50 is $40, and you save $10. You can also use "% change" with the original and discounted prices to see the percent saved.
Why do I get a different answer if I swap the two numbers in % change?
Percent change is always relative to the starting (original) value, not the ending one, so swapping which number comes first changes the base the difference is measured against. That's why a 15% increase from 200 to 230 isn't matched by an equal-sized decrease going back down.
What happens if the base number is zero?
Percent change and "X is what % of Y" are both undefined when the starting or base number is zero, since that would require dividing by zero. The calculator shows "Undefined" in that case instead of a misleading number.
How do I add or subtract a percentage from a number?
Choose "Add or subtract %", enter the number and the percentage, and pick add or subtract. The result is the number multiplied by 1 plus (or minus) the percentage as a decimal. For example, 200 plus 15% is 230, and 200 minus 15% is 170.
How do I find the original number before a percentage was added?
Divide the final amount by 1 plus the percentage as a decimal. If a total is $48.60 including 8% tax, the original was $48.60 ÷ 1.08 = $45. You can also use "X is Y% of what?" if you know the part and the percentage it represents. For example, $2.40 is 8% of $30.
What is the difference between percent change and percentage difference?
Percent change measures how much a value moved from a starting point, so the order matters. Percentage difference compares two values with no starting point by dividing their difference by their average, so the order does not matter. Use percent change for before-and-after comparisons and percentage difference when neither value is the reference.