# Tableau WINDOW_SUM() function explained with example data

The Tableau `WINDOW_SUM()` function is used to calculate the sum of the expression within the given window parameters.

The window is defined by the parameters you specify when writing the formula for the calculated field that uses this function.

This function allows you to perform a more selective sum formula than the regular `SUM()` function.

For example, you can create a Window SUM calculated field that sums the value from the first row until the current row like this:

This tutorial will help you to understand how the `WINDOW_SUM()` function works so that you can create a calculated field as in the example above.

SalesData.csv

Once the dataset has been downloaded, you can load the file to Tableau as a Text File.

Next, open the Sheet view and create a Calculated Field named `Total Sales Window SUM` with the following formula:

``````WINDOW_SUM(SUM([Total Sales]), FIRST(), 0)
``````

The `WINDOW_SUM()` function has three parameters:

• The first parameter is the field you want to compute using the function
• The second parameter is the `start` parameter. This row will be the first row computed by the function
• The third parameter is the `end` parameter. This row will be the last row computed by the function

In the example above, the `SUM()` of the `Total Sales` field is used because you need an aggregated field to perform the `WINDOW_SUM()` calculation.

Once the calculated field has been created, generate a table in your sheet with the following steps:

• Drag the `City` and `Item` variables to the Rows shelf of the sheet
• Add the `Total Sales` variable as a Text mark for the sheet

You should have the following table generated on your Tableau sheet:

Finally, left-click on the `Total Sales Window SUM` variable two times and you will see the window sum column generated in your sheet:

And with that, you’ve added the window sum column to the table.

The second and third parameters of the `WINDOW_SUM()` function are optionals. When you omit them, the calculated numbers will sum all the numbers in the view, giving the same result as the `SUM()` function:

To take full advantage of the `WINDOW_SUM()` function capabilities, you are recommended to add the `start` and `last` parameters when using the function.

You can use the `FIRST()` and `LAST()` functions to create a dynamic calculation range that gradually adds more rows to the calculation.

To add all values from the first row to the current row, use `FIRST()` and `0`:

``````WINDOW_SUM(SUM([Total Sales]), FIRST(), 0)
``````

To add all values from the current row to the last row, use `0` and `LAST()`:

``````WINDOW_SUM(SUM([Total Sales]), 0, LAST())
``````

To add the current row and the next row exclusively, use `0` and `1`:

``````WINDOW_SUM(SUM([Total Sales]), 0, 1)
``````

To add the previous row and the current row exclusively, use `-1` and `0`:

``````WINDOW_SUM(SUM([Total Sales]), -1, 0)
``````

You can try the above formula in the example workbook that you can use here:

Tableau WINDOW_SUM Example Workbook

Now you’ve learned how the `WINDOW_SUM()` function works in Tableau. Good job! 😉

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