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Percentage calculator

Work out any of the three everyday percentage questions — what X% of a number is, what percent one number is of another, or the percentage increase or decrease between two figures — without doing the arithmetic by hand.

  • Nothing you type leaves this page
  • Works offline once loaded
  • Free forever, no signup

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How to use this tool

  1. Pick the calculation you need

    X% of Y, X is what % of Y, or percentage increase/decrease between two numbers.

  2. Enter the two numbers

    The answer updates as you type — there is no button to press.

  3. Read the plain-English answer

    The result is spelled out as a sentence so it is unambiguous which number is which.

Questions people ask

How do I calculate X% of a number?

Divide X by 100 and multiply by the number — for example 20% of 200 is (20/100) × 200 = 40. The "X% of Y" mode does exactly this.

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

Divide the first number by the second and multiply by 100 — for example 40 is (40/200) × 100 = 20% of 200. That is what "X is what % of Y" mode computes.

How is percentage increase or decrease calculated?

Subtract the original value from the new value, divide by the original value, and multiply by 100. Going from 200 to 250 is a (250−200)/200 × 100 = 25% increase; going from 200 to 150 is a 25% decrease.

Why does the tool say percentage change from zero is undefined?

Percentage change measures how big the difference is relative to the starting value — and dividing by a starting value of zero has no defined answer, the same reason division by zero is undefined in ordinary arithmetic. Any increase from zero is technically an infinite percentage increase, which is not a useful number to show.

Why is the answer rounded the way it is?

Results are rounded to two decimal places for readability, avoiding the long floating-point tails (like 33.33333333333336) that raw JavaScript arithmetic sometimes produces.

Related tools

Bookmark this page — the tool keeps working offline, and your settings stay in this browser. Built by Dynamb Technologies, who make software for a living.