# Edit a Calculated Field
Calculated field values can be used in setting up your program rules, allowing for a wide range of advanced program logic. User-created [calculated fields](https://help.impact.com/brand/what-would-you-like-to-learn-about/advocate-program/manage-advocate-participants/custom-and-calculated-fields/calculated-fields-explained) can be edited at any time.
#### Edit a calculated field
1. From the left navigation menu, select  **\[Engage] → Data Sources → Fields**.
2. Hover your cursor over the field you want to edit, then select **Edit**.
* You must select a user-created calculated field. The default calculated fields cannot be edited.
3. Edit the field as required.
* You can change the event used to calculate the field and any filters or tracking windows.
* The calculated field key and calculation type cannot be changed.
4. Optionally, within the *Review* section, select  **\[Unchecked box] Recalculate values on save**.
* If your field uses a `sum` or `count` calculation, then we recommend requesting a [recalculation](https://help.impact.com/brand/what-would-you-like-to-learn-about/advocate-program/manage-advocate-participants/custom-and-calculated-fields). For other calculation types, recalculation isn't possible—refer to the [recalculation considerations](#section-idm234428141470463) before making changes.
5. Select **Save**.
#### Recalculation considerations
| If | Then | Example |
| ------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| The field does not have a tracking window or the tracking window has been **removed**. | • The previous field value will be retained and act as the starting point for the new calculation.
• The new calculation will be used moving forward.
| The field currently sums the revenue on `userPurchase` events. When you update it to sum revenue on `purchase` events instead, the existing value on a participant’s profile will be unchanged. The next time we receive a purchase event for them, the revenue amount is added to the existing value. |
| The field has an existing tracking window but the window is **unchanged**. | | |
| A tracking window is being **added to** an existing calculated field | • The previous field value will be retained only until new events come in. It will be wiped when the next matching event comes in.
• The new configuration will be used moving forward.
• Request a recalculation if you want to take historical data into account with the new configuration.
| The field counts the number of purchases a participant makes. If you add a tracking window for a month, the existing value on the participant’s profile is wiped when the next purchase event comes in.
A participant who made 5 purchases would have a value of 5 prior to your edits. The next time this participant makes a purchase, the old value is wiped and the field value is set to 1.
|
| The field has an existing tracking window that is being **edited**. | • When editing an existing window on a calculation field, be sure to recalculate.
• Editing without recalculation can have adverse effects on the participant's field value.
| You change your tracking window from a fixed window to a sliding window. |
| The field has an existing sliding window and the **maximum calculation value is changed**. | • The new configuration will be applied to participants’ historical data when the next matching event comes in.
• Request a recalculation to update the field value without waiting for new events.
| The windowed field currently counts the number of purchases a participant has made, to a maximum value of 10. When the max changes to 5 and a new purchase event comes in for that participant, the maximum of 5 will be retroactively applied to the data within the window. |
{% hint style="warning" %}
**Warning:** The value of a windowed calculated field can’t be manually overwritten via API. You will receive an error message if you send us data that would overwrite an existing value.
{% endhint %}