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I am trying to get the weighted avg of percentages in excel. I have followed multiple mathematical examples and excel examples all over the web and I still have not got a clear answer when you have two factors or criteria that make up the percentage.

1.) I am calculating Growth Rate from month to month. So each month has a different growth rate or percentage.

2.) So I have 2 Columns. 'START'(A) to indicate total number of people at start of the month and 'END' (B) to indicate the total number of people at the end of the month.

3.) A and B = Growth Rate or percentage which is in Column C. The formula used to calculate the growth rate is (A-B)/A

How do I get the weighted average? What is the correct math to use?

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Ross Millikan
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Jay26
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    Weighted by what? You have to say what the weights are to be. For example, you could be weighting by the people at the beginning of the month, or the people at the end of the month, or by something entirely different, like the number of days in the month. – saulspatz Sep 05 '18 at 01:43
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    Weighted average of what? Weighted by what? Your growth rates have the wrong sign as in the first line the number decreases so the rate should be negative – Ross Millikan Sep 05 '18 at 01:44
  • Sorry. I am calculating the number of clients that are active at the start of the month vs the end of the month. So the numbers go up and down as some clients leave or are non active. Ross you are correct I calculated the growth rate in correctly. – Jay26 Sep 06 '18 at 03:27

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Just for the fun of answering this question lingering in the dark almost forgotten after 5 years. ;)

Here is an example in Python https://hinty.io/rivashchenko/weighted-average-python/

Your limited data example of growth percentages, could be weighed by the values from the start or end column. So weighing by the start values gives this result

picture of excel file

This is a youtube video about weighted mean https://www.youtube.com/watch?app=desktop&v=8mhVQU-ZX8I

ps1
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