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Marvin's Toolbox.

Percentage Calculator

Answer any percentage question as you type: what is X% of a number, what percent one number is of another, the percentage increase or decrease between two values, a number raised or lowered by a percent, and the whole behind a part.

Runs entirely in your browser. Nothing you put in here gets uploaded.

Rounding

Decimal places for every result below. Auto keeps two and adds more when a value would otherwise round to nothing.

Percent of a number

The tip, tax and discount question.

What is
%
of?
Result
30

What percent is it

Turn a part of a whole, like a score or a share, into a percent.

is what percent of?
Result
12.5%

Find the whole

Reverse a percentage, like getting back to the price before a discount.

is
%
of what number?
Result
200

Percentage change

How much a value grew or shrank, measured against where it started.

Fromto
Changean increase of 30
+25%

Increase or decrease

Raise and lower a number by a percent, both answers at once.

Takeand change it by
%
Increased+20
220
Decreased-20
180

Percent difference

How far apart two values are, with neither treated as the start. For a before and after, use the percentage change above.

compared with
Difference
18.18%

About the Percentage Calculator Tool

This tool answers the everyday percentage questions in one place. Every card is one question written out as a sentence: take a percent of a number, work out what percent one number is of another, find the whole behind a part, measure the change between two values, or raise and lower a number by a percent.

Each card starts with a small worked example so you can see how it behaves, and every answer has its own copy button. A rounding control at the top sets how many decimal places you get.

What you can do

  • Work out what a percent of a number is, for tips, tax and discounts.
  • See what percent one number is of another.
  • Find the original whole from a part and its percent, like a price before a discount.
  • Calculate the percentage increase or decrease from one value to another.
  • Raise and lower a number by a percent and read both results at once.
  • Compare two values with the symmetric percent difference.

How to use the Percentage Calculator

  1. 1Pick the card that asks your question.
  2. 2Type your numbers into the blanks. The answer updates as you type.
  3. 3Copy a result with the button next to it.
  4. 4Adjust the rounding at the top if you need more or fewer decimal places.

Percentage change or percent difference?

Percentage change compares a start value with an end value, so the direction matters. Going from 100 to 120 is a 20% increase, but going from 120 to 100 is a 16.67% decrease, because each change is measured against its own starting point. Percent difference ignores direction. It divides the gap between two values by their average, so 100 and 120 are 18.18% apart no matter which comes first. Use change for a before and after, and difference when neither value is the baseline.

One formula, three questions

The first three cards are the same relationship seen from three sides: the part equals the percent times the whole. Give any two of those numbers and the third follows. 15% of 200 is 30, so 30 out of 200 is 15%, and if 30 is 15% of something, that something is 200.

Discounts, tips and other daily sums

For a 20% tip on a 45 bill, the first card gives the tip itself and the increase result gives the total with the tip included. For 30% off an 80 price, the decrease result is what you pay. To undo a percentage, use the find the whole card: if a sale price of 56 is 70% of the original, the original was 80. The same cards cover VAT, raises, interest and test scores.

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