Percentage Calculator

About this calculator

This calculator handles six common percentage tasks in one place: finding what X% of a number is, figuring out what percentage one number is of another, finding the original number when you know X is P% of it, calculating the percentage change between two values, measuring the percentage difference between two values, and adding or subtracting a percentage from a base number. Type into any card and the answer updates instantly.

How to read your results

The page is split into six independent mode cards, each solving a different percentage question. Each card shows two input fields and displays its result — or a short note if the inputs are incomplete or mathematically impossible — directly below the fields. All six modes work simultaneously, so you can use as many at once as you like.

Worked example

Enter 15 in the percent field and 80 in the number field of the "What is X% of Y" card. In the "Add / subtract a percent" card, enter 80 as the base and 15 as the percent.

15% of 80 is 12. Adding 15% to 80 gives 92, and subtracting 15% from 80 gives 68 — confirming all three results are consistent.

Frequently asked questions

What is the difference between percentage change and percentage difference?

Percentage change measures a directional shift from an old value to a new one: ((new − old) / |old|) × 100. It has a sign — positive for an increase, negative for a decrease. Percentage difference, by contrast, is order-independent: it divides the absolute gap by the average of the two values, giving a symmetric measure that does not imply direction.

Why does the "X is what % of Y" card refuse to calculate when Y is zero?

The formula is (X / Y) × 100. Division by zero is undefined, so the calculator shows a note rather than an error or an infinite result. Make sure the denominator is a non-zero value.

Can I use these formulas for discounts, tips, or tax?

Yes. To find a discount amount, use "What is X% of Y" with X as the discount rate and Y as the original price. To find the price after a percentage off or on, use "Add / subtract a percent." The same logic applies to tips, VAT, or any markup.

How do I calculate X% of Y?

Multiply the whole by the percentage written as a decimal: Y × (X / 100). For example, 20% of 50 is 50 × 0.20 = 10. The "What is X% of Y" card does this for any two numbers.

How do I find a percentage increase or decrease?

Subtract the old value from the new one, divide by the old value, and multiply by 100: ((new − old) / old) × 100. Going from 100 to 125 is a 25% increase; going from 50 to 40 is a 20% decrease. A positive result is an increase, a negative one a decrease.

X is what percent of Y?

Divide the part by the whole and multiply by 100: (X / Y) × 100. For example, 12 is 15% of 80 because 12 / 80 = 0.15. Use the "X is what % of Y" card, keeping the whole (Y) non-zero.

X is P% of what number?

Divide the part by the percentage written as a decimal: X / (P / 100). For example, 25 is 50% of 50 because 25 / 0.50 = 50, and 15 is 30% of 50 because 15 / 0.30 = 50. Use the "X is P% of what" card, keeping the percent (P) non-zero so the base is defined.

How it's calculated

Each mode uses a direct formula. "What is X% of Y" computes (X / 100) × Y. "X is what % of Y" computes (X / Y) × 100, requiring Y ≠ 0. "X is P% of what" solves for the base as X / (P / 100), requiring P ≠ 0. Percentage change is ((new − old) / |old|) × 100, signed, requiring the old value ≠ 0. Percentage difference is |A − B| / ((|A| + |B|) / 2) × 100, order-independent, requiring the two values not both be zero. "Add / subtract a percent" gives base × (1 + p / 100) and base × (1 − p / 100). All formulas follow standard mathematical definitions as documented on MathIsFun.

Sources

• www.mathsisfun.com/percentage.html
• www.mathsisfun.com/numbers/percentage-change.html
• www.mathsisfun.com/percentage-difference.html

Reviewed by the YouCalc Team · Last reviewedJune 11, 2026