I have a basic formula field in my child object:
IF(AND( Date__c = (today()-365)),1,0)
This is basically looking at a record and looking if it is in the last 12 months and then showing a 1 or a 0. I have tried this with a true / false as well.
The formula works great and shows a 1 or 0 when it is within a 12 month period. However i now want to do a roll up summary to the parent object. However when i do a sum and go to chose this field as a roll up filter field it isnt there to choose? I cannot work out why as all my other Numeric formula fields are there and it doesnt reference any external objects... Any ideas as i'm well and truly stumped