Freeze a column value when item is Done

I would like to keep a record of how long it took an item to go from “Creation at” to when it’s marked “Done”.

I have a formula column that calculates the difference between Today’s date the “Created at”. If I wanted to freeze that number and put it in a new column, what would that automation look like?

Also open to other ways to accomplish the same thing. Seems like a simple/common objective so I was surprised to not find anything about it in the community. Thanks!

Hi @will_b - I would create a new date column called “Completed Date” with an automation:
When Status changes to Done, Set Completed Date to Today

Then you can use your formula column to calculate the days between the Creation Date and Completed Date.