We can apply the Average function to easily calculate the moving average for a series of data at ease. Please do as follows:

1. Select the third cell besides original data, says Cell C4 in our example, and type the formula =AVERAGE(B2:B4) (B2:B4 is the first three data in the series of data) into it, and the drag this cell’s AutoFill Handle down to the range as you need. See screenshot:
Note: We need to calculate the moving average with the interval of 3 data, therefore we enter the formula into the third cell.

2. Keep selecting these formula cells, and click the Decrease Decimal button to adjust the decimal places of moving average results as you need. See screenshot:

Tip: Save a range as AutoText entry (remaining cell formats and formulas) for reusing in future

Kutools for Excel provides a cute workaround of AutoText utility to to save the range as an AutoText entry, which can remain the cell formats and formulas in the range. And then you can reuse this range with just one click in any workbook.

Excel 2010 and 2013's Data Analysis command supports us a group tools of financial and scientific data analysis, including the Moving Average tool which can help you to calculate the average of a specific range and create a moving average chart easily.

1. Click the File > Options.

2. In the Excel Options dialog box, click the Add-Ins in the left bar, Keep Excel Add-Ins selected in the Manage box and then click the Go button.

3. In the opening Add-Ins dialog box, check the Analysis ToolPak in the Add-Ins available box, and click the OK button.

4. Now you get back to the main interface of Excel. Click the Data > Data Analysis.

5. In the popping up Data Analysis dialog box, click to highlight the Moving Average in the Analysis Tools box, and click the OK button.

6. Now in the throwing out Moving Average dialog box, please:

(1) Put cursor into the Input Range box, and then select the range you want to calculate the moving averages. In our case, we select the Range B2:B13.
(2) In the Interval box, enter the interval you want to calculate moving averages based on. In our case, we enter 3 into it.
(3) Put cursor into the Output Range box, and then select the range you want to output the moving averages. In our case, we select the Range C2:C13.
(4) Check the Chart Output option, and click the OK button.

Now you will get the moving averages in the specified cells, meanwhile, a moving average chart is created besides the moving averages. See screen shot below:

Note: This method does not work in Excel 2007 because the Analysis ToolPak is not available in Excel 2007.

If you have created a column chart in Excel before, you can add a moving average trendline for this existing chart easily as following:

1. Select the chart, and then click the Design > Add Chart Element > Trendline > More Trendline Options in Excel 2013.

Notes:
(1) If you do not need to specific the interval of moving averages, moving average names, etc., you can click the Design > Add Chart Element > Trendline > Moving Average directly.
(2) In Excel 2007 and 2010, you can click the Layout > Trendline > More Trendline Options.

2. In the opening Format Trendline dialog box/pane, check the Moving Average option and specify the Interval of moving average in the Period box. See screen shots:

Excel 2013 and higher version:

Excel 2007 and 2010:

3. Close the Trendline dialog box/pane. Now you will see the moving average trendline is added in the column chart. See below screen shot:

Average range with rounding in Excel

Weighted average in Excel

Calculate average/compound annual growth rate in Excel

Running total /average in Excel