Hi @laurenp ,
I'm not very familiar with SP List expressions, but apparently there is a way to create a calculated field to capture this day difference.
In any case, I will share with you a Power Automate solution for that. You just need to create a recurrent flow to run in a daily basis and contains the following actions:
List overview
For this example, I will be using this SP List, which basically track the days since a task was created (the logic is the same for your use case):
Step 1: Get items from list
Pull all records from your list (you can apply any filters if you need it). You can do it by using the action 'Get items'.
Step 2: Timespan variable
The dateDifference expression in Power Automate returns a timespan, which has a string datatype. We will need to store it in a variable and process it before update the SP List.
Step 3: Loop records and capture timespan
Then you will need to loop all of the records from your 'Get items' action and store the dateDifference in timespan variable. For doing this, you will use this expression: dateDifference(items('Apply_to_each')?['Starttime'], utcNow()). Make sure to change the bolded text to your actual "start date" column name.
The output from dateDifference will be something similar to it. The amount before the first '.' (29) is the quantity of days between the 2 dates:
Step 4 (final): Update the list
Finally, you call the 'Update item' action inside the loop to update your List record. Make sure to pass all again all the field values as input (ID to ID, Title to Title, and so on): if you ignore it, the fields will be overwritten with blanks.
For your "date difference" column, you will use this expression: Int(first(split(variables('timespan'), '.'))). We are basically splitting the timespan by the '.', catching the first part of it text (the qty of days) and converting to an integer (I'm assuming here that your list column contains a numeric data type).
Let me know if it works for you or if you need any additional help!
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