Excel automatically updates SUM formulas whenever the data they reference changes. There's no need for a special setting to enable this.

Here's how it works:

* Basic SUM Formula: Let's say you have numbers in cells A1 to A10 and you want their sum in cell B11. You can simply enter the formula `=SUM(A1:A10)` in B11.
* Data Changes: If you edit any value within the range A1:A10 (e.g., changing the value in A5), the SUM in B11 will automatically recalculate and reflect the updated total.

Tips for Automatic Updates:

* Ensure Correct Range: Double-check that your SUM formula references the correct range of cells you want to add.
* Avoid Manual Edits: While the formula updates automatically, directly editing the value in the cell containing the SUM formula (B11 in our example) will break the automatic update. Edit the data within the referenced range (A1:A10) for the SUM to adjust.
* Formula References: If your SUM formula references other cells containing formulas, those formulas need to be set up to update automatically as well (dependent on their own referenced cells).

Advanced Scenarios:

* New Rows/Columns: By default, SUM formulas will only update if changes occur within the defined range. If you plan to insert new rows or columns where you want to include data in the sum, there are a couple of approaches:
* Include Empty Cell: Leave an empty cell at the end of your initial range (e.g., A11) when defining the SUM formula (`=SUM(A1:A11)`). As you insert new data rows, the formula will automatically expand to include them.
* OFFSET Function: For more dynamic scenarios, you can use the OFFSET function within your SUM formula to adjust the reference range based on another cell value. This requires a deeper understanding of Excel functions.

For most cases, the basic SUM formula will automatically update as your data changes. If you encounter situations where the automatic update isn't working as expected, check the points mentioned above to identify potential causes.