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Percentage Calculator

Solve common percentage problems: what is X% of Y, percent change, and more.

Mode

Inputs

Formula: (X ÷ 100) × Y = result

Result

% of value
30
20% of 150

What is the Percentage Calculator?

A percentage calculator is a free online tool that solves the four most common percentage problems: what is X% of Y, X is what percent of Y, the percent change between two values, and increase or decrease a value by X%. Use it for discounts, tips, taxes, grades, and growth rates.

Percentage Calculator formula

To find X% of Y: result = (X ÷ 100) × Y. To find what percent X is of Y: % = (X ÷ Y) × 100. Percent change from X to Y = ((Y − X) ÷ X) × 100 — positive means increase, negative means decrease. To increase or decrease Y by X%: result = Y × (1 ± X/100).

How to use the Percentage calculator

  1. 1Choose the mode that matches your problem: '% of value', '% of total', '% change', or '± %'.
  2. 2Enter the two values the mode asks for (e.g., the percentage X and the base value Y).
  3. 3For 'Increase / decrease', also pick the direction (+ to grow, − to shrink).
  4. 4Read the result, the worked formula, and the plain-language summary.
  5. 5If you compute percent change from 0, the calculator shows '—' with a 'Starting value (X) must be non-zero' hint (dividing by zero is undefined).

Example calculation

What is 15% of 200? result = (15 ÷ 100) × 200 = 0.15 × 200 = 30. So 15% of 200 is 30. The steps panel also displays the decimal form (0.15) and the formula '(X ÷ 100) × Y = result'.

Frequently asked questions

How do I calculate percentage increase?
Use the formula ((new − old) ÷ old) × 100. For example, a price going from $80 to $100 is ((100 − 80) ÷ 80) × 100 = 25% increase. Switch to the '% change' mode, enter X = 80 and Y = 100, and the calculator returns '▲ 25% increase'.
What is the percent change formula?
Percent change = ((new value − old value) ÷ old value) × 100. A positive result is an increase; a negative result is a decrease. The old value must be non-zero — percent change from 0 is mathematically undefined (infinite).
How is percentage difference different from percentage change?
Percentage change compares one value to a fixed baseline (old → new) and is directional. Percentage difference compares two values with no clear baseline and uses their average as the denominator: |a − b| ÷ ((a + b)/2) × 100. This calculator computes percentage change; for a difference, average the two values yourself and use the '% of total' mode.
Can I calculate a discount or tip percentage?
Yes. For a 20% discount on a $50 item, use '± %' mode with Y = 50, X = 20, and direction − → result $40 (the discount is $10). For an 18% tip on a $32 check, use '% of value' with X = 18 and Y = 32 → $5.76.
Why does the calculator show '—' for percent change from zero?
Percent change divides by the starting value, so starting from 0 means dividing by 0, which is undefined (approaches infinity). Rather than displaying 'Infinity', the calculator shows '—' with the hint 'Starting value (X) must be non-zero'.

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