Three percentage calculations that solve everyday questions

Percentages appear in discounts, budgets, reports, schoolwork, and price changes. The calculation changes depending on which number is the starting point. Choose the question first, then supply the values.

What is X percent of Y?

Multiply Y by X and divide by 100. For example, 20% of 150 is 30, because 150 × 20 ÷ 100 = 30. A 20% discount on 150 therefore removes 30; the price after this discount is 120 before any tax or other charges. In the percentage calculator, choose “X% of Y” for the discount amount.

X is what percent of Y?

Divide X by Y and multiply by 100. If 30 of 150 tasks are complete, then 30 ÷ 150 × 100 = 20%. The second number is the base. The base cannot be zero for this question, so the tool reports an error when it is.

What changed from X to Y?

Subtract the old value X from the new value Y. Divide by the absolute value of X, then multiply by 100. A move from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%. A move from 100 to 80 is −20%. The two numbers are different because they use different starting values.

If the old value is zero, percentage change is undefined: there is no nonzero baseline to divide by. If you work with negative starting values, state your convention explicitly; our tool uses the absolute starting value as the denominator. For business reports, show the original and new numbers alongside the percent so readers see the scale of the change.

Check the real-world rules

Calculating a percentage is only part of a tax, loan, or financial decision. Compounding periods, exclusions, rounding rules, and local law can change the amount due. Use the result as arithmetic and verify the rules that apply to your situation. The calculator runs locally in your browser and does not send the numbers to our server.