Two indispensable formulas for percentages

Two indispensable formulas for percentages

Created:15 Jul 2020 11:21:05 , in  Maths

In this article I look at two very useful mathematical formulas related to dealing with percentages efficiently. You might know them, but it is likely, you haven't not been shown at least one of them while studying the subject during your school years. I remember my own struggles with percentages, a lot of them due to not knowing these formulas in the form I'm presenting in this article.

Percentages formula 1

y = ( x / 100 ) * z 

This formula tells you that y is x% of z, where x, y and z are numbers.

Here is an example how to use it:

Example: Suppose, that you have a file with 1084 lines of code and comments in it. Somebody who created the file told you that 25% of the lines are comments. You want to know the exact number of lines which contain comments.


z = 1084
x = 25
y = ?

y = (25 / 100) * 1084 = 271

So, 25% of 1084 is 271, which is the number of comments in the file.

Percentages formula 2

y  =  ( 1 + x / 100 ) * z

This formula tells you, that y is x% larger than z, where x, y and z are numbers.

Example: Suppose, that your friend has just told you that his website log file's size month-on-month growth is on average 7% and that log file size for the last month was 124MB. You want to know what in terms of the file size your friend might expect at the end of this month.

x = 7
z = 124
y = ?

y = (1 + 7 / 100) * 124 = 132.68MB

So the total log file size for this month is likely to be 132.68MB.


Both formulas given in this articles are incredibly useful when dealing with all sorts of percentages related questions. They are easy in themselves, so also easy to transform and turn into functions written in a programming language.

I hope you have found this article interesting. If you have something to add, you are welcome to leave a comment below.

This post was updated on 15 Jul 2020 11:30:24

Author, Copyright and citation


Sylwester Wojnowski

Author of the above article, Sylwester Wojnowski, enjoys sWWW writing computer code in PHP, JavaScript and BASH, and some other things he wrote more on on the About page of this website.


©Copyright, 2020 Sylwester Wojnowski. This article may not be reproduced or published as a whole or in parts without permission from the author. If you share it, please give author credit and do not remove embedded links.

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Cite this article as:

Wojnowski, Sylwester. "Two indispensable formulas for percentages." From sWWW - Code For The Web .

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