Percentage Calculator

Work out percentages every way: X percent of Y, what percent X is of Y, and percentage increase or decrease. Fast, free, and 100% in your browser.

% of is

is this percent of

—

Enter a value greater than zero to divide by.

Change from to

—

An increase.

A decrease.

No change.

The original value can't be zero — percentage change is undefined from zero.

Every calculation runs entirely in your browser — nothing you type is sent anywhere.

What this percentage calculator does

A percentage is simply a number expressed as a fraction of 100 — the word comes from the Latin per centum, meaning "by the hundred." This calculator covers the three questions people actually ask about percentages, so you don't have to remember which formula goes where:

  • What is X% of Y? — find a percentage of a number (e.g. 20% of 150).
  • X is what percent of Y? — express one number as a percentage of another (e.g. 30 out of 150).
  • Percentage change from A to B — measure an increase or decrease between two values (e.g. a price going from 100 to 125).

Pick a mode from the dropdown, type your two numbers, and the answer updates instantly. There is no "calculate" button to press and nothing to submit.

How to use this calculator

Choose the calculation you need from the menu at the top. Each mode shows two input boxes with plain-language labels so you always know which number goes where. Decimal values are fine (try 12.5 or 0.75), and negative numbers work too for percentage-change calculations. The result restates your inputs above the answer so you can double-check that you entered them the right way round.

The formulas behind each mode

All three modes rest on the same idea — a part divided by a whole, scaled by 100.

  • X% of Y: result = Y × (X ÷ 100). For example, 20% of 150 = 150 × 0.20 = 30.
  • X is what percent of Y: result = (X ÷ Y) × 100. For example, 30 out of 150 = (30 ÷ 150) × 100 = 20%.
  • Percentage change from A to B: result = ((B − A) ÷ |A|) × 100. A positive result is an increase; a negative result is a decrease. For example, going from 100 to 125 = ((125 − 100) ÷ 100) × 100 = +25%.

Percentage change divides by the original value, not the new one, which is why the same absolute jump can give different percentages depending on your starting point. Note also that a 25% increase followed by a 25% decrease does not return you to where you started (100 → 125 → 93.75), because each percentage is taken from a different base.

Worked example: a discount

Suppose a jacket normally costs $80 and is marked "25% off." Using the first mode, 25% of 80 is $20, so the discount saves you $20 and you pay $60. If instead you only knew the old and new prices — $80 down to $60 — the third mode confirms the change: (60 − 80) ÷ 80 × 100 = −25%, a 25% decrease. And if you wanted to know what fraction of the original price you actually paid, the second mode gives 60 out of 80 = 75%.

A note on accuracy

Results are rounded to at most four decimal places for readability, so a repeating decimal such as 1 out of 3 shows as 33.3333% rather than the exact value. Divide-by-zero cases — asking what percent a number is of zero, or the percentage change from an original value of zero — are mathematically undefined, and the calculator says so instead of showing a misleading number.

References

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