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Percentage calculator

Four percentage operations, computed instantly in your browser, nothing leaves your device.

How Percentage calculator works

The percentage calculator covers the four everyday percentage questions in one screen: what is X percent of Y, X is what percent of Y, the percentage change from one value to another, and increasing or decreasing a value by a given percentage. Pick the mode, type two numbers, and the answer appears immediately. All arithmetic runs locally in your browser with no data sent anywhere.

Decimals and negative numbers are accepted throughout, so the change mode correctly handles a drop from a negative starting value, and the increase or decrease mode doubles as a quick discount, markup or tax helper.

Written by Bastien Sulyan

How to use Percentage calculator, step by step

  1. Choose the calculation mode: "X% of Y", "X is what % of Y", "% change", or "increase/decrease by %".
  2. Enter the two values required for that mode.
  3. Read the result instantly from the output field.
  4. Switch to a different mode at any time without clearing your numbers.

Common use cases

  • Checking what 15 percent tip on a 47 dollar meal comes to before you go to the table.
  • Calculating a 20 percent discount on a retail price to know how much you actually save.
  • Measuring the percentage change in monthly sales revenue from one period to the next.
  • Finding what markup to apply to a wholesale cost to reach a desired retail price.

Frequently asked questions

Does this calculator send my numbers to a server?

No. All the arithmetic runs locally in your browser. Nothing you type is uploaded or stored anywhere. You can disconnect from the internet after the page loads and the calculator keeps working.

How is percentage change calculated?

Percentage change from X to Y is (Y minus X) divided by the absolute value of X, then multiplied by 100. A rise gives a positive result and a fall gives a negative result, even when X is a negative number. Example: from 80 to 100 is (100 minus 80) divided by 80, times 100 = 25 percent increase.

What does increase or decrease by percent do?

Applying a percentage to a base value: increase multiplies the base by (1 + p divided by 100), decrease multiplies by (1 minus p divided by 100). Example: decreasing 200 by 30 percent gives 200 times 0.70 = 140.

What is the formula for X is what percent of Y?

It is (X divided by Y) times 100. Example: 35 is what percent of 140? Answer: 35 divided by 140 times 100 = 25 percent.

Can I use decimals and negative numbers?

Yes. Enter any decimal such as 12.5 or a negative starting value such as minus 40. The percentage change formula uses the absolute value of X in the denominator, so a move from minus 40 to minus 30 is (minus 30 minus minus 40) divided by 40 times 100 = 25 percent change.

Does the calculator work offline?

Yes. Once the page has loaded the tool runs with no internet connection. All four percentage modes are plain arithmetic executed inside your browser tab, which is also why your numbers never leave your device.

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