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zacdaddytools

Percentage Calculator

Work out percentages, increases and decreases instantly.

Choose a calculation

Select what you want to work out, then enter your numbers.

Calculated instantly

What is X% of Y?

%

Result

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Enter both numbers to see the result and calculation.

Four common percentage calculations

Choose the calculation that matches your question: find a percentage of a number, find what percentage one value represents of another, measure an increase, or measure a decrease. The labels and explanation change with the selected mode so the order of the numbers stays clear.

Results support decimal and negative values where the underlying calculation is valid. Up to six decimal places are displayed when needed, avoiding unnecessary trailing digits for simple answers.

Formulas with quick examples

To find X% of Y, divide X by 100 and multiply by Y. To find what percentage X is of Y, divide X by Y and multiply by 100. Percentage change compares the difference with the absolute value of the original number.

Three useful examples

15% of 80 = 0.15 × 80 = 12.

30 is what percentage of 120? 30 ÷ 120 × 100 = 25%.

An increase from 50 to 65 is 15 ÷ 50 × 100 = 30%.

Avoid common percentage mistakes

A percentage change needs a meaningful original value. If the original or comparison total is zero, division is undefined and the calculator cannot produce a percentage. Also remember that increasing by 20% and then decreasing by 20% does not return to the starting number because the second change uses a different base.

FAQs

Questions about the percentage calculator

How do I find 20% of a number?

Choose “Percentage of”, enter 20 as the percentage and the other value as the number. The formula is 0.20 multiplied by the number.

How do I find what percentage one number is of another?

Choose “Find percentage”, enter the part first and the total second. The calculator divides the part by the total and multiplies by 100.

What is the percentage increase formula?

Subtract the original from the new value, divide the difference by the absolute original value, then multiply by 100.

Why can the original number not be zero?

Percentage change uses the original as a divisor. Division by zero has no defined result.