I have a calendar list in which to post deadlines. I need a reminder to be sent out two weeks before the deadline, so I am trying to put in a retention policy. To measure the date to activate this retention stage I have created a calculated column that removes 14 days from the end time. This works fine, however, I cant see this column as an option to activate the retention stage. Am I missing something? Thanks.
No you're not. Retention policies won't recognise a calculated date even if it's set to date/time format.
A good way around this is to shift the date calculation into SharePoint Designer. Use the "Add Time to" action to subtract 14 days (-14) from your deadline day and output this to a variable. In the next step, pause the workflow until then and your workflow will wait until then to trigger.
You'll have to compose the email also in the last step but I've always found this an effective workaround.