how to calculate a running average in excel

Understanding trends in your data is crucial for making informed decisions, whether you're analyzing stock prices, sales figures, or scientific measurements. One of the most effective ways to smooth out fluctuations and reveal underlying patterns is by calculating a running average, also known as a moving average. This guide will walk you through various methods to calculate a running average in Excel, from simple formulas to advanced tools, and even provide a handy interactive calculator.

What is a Running Average?

A running average is a series of averages of different subsets of the full data set. Each subset, or "window," is of a specified size (e.g., 3-day, 5-period), and it "moves" forward in the data, typically by one period at a time. For example, a 3-period running average would calculate the average of the first three data points, then the average of the second, third, and fourth data points, and so on.

Why Use a Running Average?

• Trend Identification: It helps to smooth out short-term fluctuations and highlight longer-term trends or cycles in your data.
• Noise Reduction: By averaging over a period, random variations (noise) in the data are reduced, making the true signal more apparent.
• Forecasting: Running averages can be used as a simple forecasting tool, predicting future values based on past performance.
• Data Comparison: It provides a standardized way to compare different time series or datasets.

Method 1: Simple Running Average using the AVERAGE Function (Fixed Window Size)

This is the most straightforward method for calculating a running average when your window size is fixed and you want to apply a simple formula.

Step-by-Step Example:

1. Prepare Your Data: Let's assume your data points are in column B, starting from cell B2.
2. Set Up Your Headers: In cell C1, you might type "3-Period Running Average" (or whatever your window size is).
3. Enter the First Formula: If you want a 3-period running average, the first average can only be calculated once you have 3 data points. So, in cell C4 (assuming your data starts at B2, the average of B2, B3, B4 would go here), enter the formula:

   =AVERAGE(B2:B4)

   This calculates the average of the first three values (B2, B3, B4).
4. Drag Down the Formula: Select cell C4, then click and drag the fill handle (the small square at the bottom-right corner of the cell) down column C. Excel will automatically adjust the cell references for each subsequent row.
   • In C5, the formula will become =AVERAGE(B3:B5).
   • In C6, it will be =AVERAGE(B4:B6), and so on.
   This creates your running average series.
5. Handle Initial Rows: The first few rows (e.g., C2 and C3 for a 3-period average) will remain blank or contain errors because there aren't enough preceding data points to form a full window. This is normal behavior for a trailing running average.

Method 2: Dynamic Running Average using `OFFSET` (Variable Window Size)

If you want the flexibility to change the running average window size without modifying every formula, the OFFSET function is incredibly powerful. This method is for a trailing running average, meaning the average includes the current data point and the `N-1` preceding data points.

Understanding `OFFSET`

The OFFSET function returns a range that is a specified number of rows and columns from a starting reference cell. Its syntax is:

OFFSET(reference, rows, cols, [height], [width])

• reference: The cell or range from which to offset.
• rows: The number of rows, up or down, that you want the top-left cell of the result to refer to.
• cols: The number of columns, to the left or right, that you want the top-left cell of the result to refer to.
• [height]: (Optional) The height, in rows, that you want the returned range to be.
• [width]: (Optional) The width, in columns, that you want the returned range to be.

Step-by-Step Example:

1. Prepare Your Data: Data in column B, starting from B2.
2. Define Window Size: Dedicate a cell, say D1, to enter your desired window size (e.g., 3 for a 3-period average). Make sure to use absolute references for this cell (e.g., $D$1).
3. Enter the Dynamic Formula: In cell C2 (or the first row where you want to start calculating), enter the following formula and drag it down:

   =IF(ROW()-ROW($B$2)+1 < $D$1, "", AVERAGE(OFFSET(B2, -($D$1-1), 0, $D$1, 1)))

4. Explanation of the Formula:
   • ROW()-ROW($B$2)+1 < $D$1: This part checks if there are enough data points available to calculate a full running average window. ROW()-ROW($B$2)+1 gives the current data point's index within your dataset (1 for B2, 2 for B3, etc.). If this index is less than your specified window size (e.g., for a 3-period average, the first two points won't have enough data), it returns an empty string ("").
   • AVERAGE(...): If there are enough data points, it calculates the average of the range defined by OFFSET.
   • OFFSET(B2, -($D$1-1), 0, $D$1, 1):
     • B2: The reference point is the current cell in your data column.
     • -($D$1-1): This moves the starting point of the average window up by `window_size - 1` rows. For a 3-period average (`$D$1=3`), it moves up by 2 rows, so the average starts 2 rows before the current row.
     • 0: Stays in the same column.
     • $D$1: The height of the range is the window size itself.
     • 1: The width of the range is 1 column.

Now, you can simply change the value in cell D1, and your entire running average column will update automatically!

Method 3: Using Excel's Data Analysis Toolpak (Moving Average)

For a more automated approach, especially if you need to analyze multiple series or want additional statistics, Excel's built-in Data Analysis Toolpak is very useful. It calls a running average a "Moving Average."

Enable the Data Analysis Toolpak:

1. Go to File > Options.
2. Select Add-ins from the left pane.
3. At the bottom, select Excel Add-ins from the "Manage" dropdown and click Go....
4. In the Add-ins dialog box, check Analysis Toolpak and click OK.
5. You should now see a "Data Analysis" option in the Data tab of the Excel Ribbon.

Calculate Moving Average with Toolpak:

1. Go to the Data tab and click Data Analysis.
2. From the list, select Moving Average and click OK.
3. Input Range: Select the range of your data (e.g., $B$2:$B$100). Include the header if you check "Labels in first row."
4. Interval: Enter your desired window size (e.g., 3 for a 3-period average).
5. Output Range: Specify where you want the results to appear (e.g., $C$1).
6. Chart Output (Optional): Check this box if you want Excel to automatically generate a chart with both your original data and the moving average.
7. Click OK.

The Toolpak will generate the running average values. Note that it will leave the initial rows blank, similar to the formula methods, as there isn't enough data to form a full window.

Method 4: Visualizing with Charts (Adding a Moving Average Trendline)

Sometimes, you don't need the actual running average values in a column, but rather want to see the trend directly on a chart.

1. Create a Chart: Select your data range (e.g., column B) and insert a Line Chart (Insert > Charts > Line Chart).
2. Add Trendline:
   • Click on the chart to select it.
   • Click the '+' (Chart Elements) button that appears next to the chart.
   • Hover over Trendline and click the arrow next to it.
   • Select More Options....
3. Configure Trendline:
   • In the "Format Trendline" pane, select Moving Average.
   • Set the Period to your desired window size (e.g., 3).

Excel will add a moving average line directly onto your chart, providing a visual representation of the trend without needing a separate column for calculations.

Tips for Success with Running Averages

• Choosing the Right Window Size: The window size (or "period") is critical. A smaller window (e.g., 3 periods) will react quickly to changes but might still show some noise. A larger window (e.g., 10 or 20 periods) will produce a smoother line, better for long-term trends, but will lag behind recent changes. Experiment to find what best suits your data and analytical goals.
• Handling Missing Data: If your dataset has blank cells or text, Excel's AVERAGE function will ignore them, which is generally desirable. However, be mindful if a significant number of missing values could skew your average.
• Interpretation: A running average is a lagging indicator. It reflects past data, so while it shows trends, it doesn't predict future exact values, only potential direction based on past patterns.

Conclusion

Running averages are an indispensable tool in data analysis, helping you transform raw, noisy data into clear, actionable insights. Whether you prefer the simplicity of the AVERAGE function, the flexibility of OFFSET, the automation of the Data Analysis Toolpak, or the visual appeal of chart trendlines, Excel provides robust options for calculating and interpreting these powerful metrics. Start applying them to your datasets today to uncover hidden trends and make smarter decisions!