To calculate a running average, or a moving average, for a range of cells (a column), you use the AVERAGE function. The only trick you need to apply is to make your range changing continuously.
In the example below we want to calculate the running average of the sales from January to June.
Our ranges for the months will be as follows:
January – one cell : B2:B2
February- 2 cells B2:B3
March – 3 cell2: B2:B4 … and so on.
The first cell of the range is always the same for all months : B2, so we will make it absolute reference like this: $B$2. Therefore our formulas , in C column will be like this:
March: =AVERAGE($B$2:B4) …. Ans so on.
Enter the first formula in cell C2 and autofill down the rest of the range.