Hi,

I work for a charity that distributes surplus food to members of the local community for a small weekly fee. I use Airtable to keep track of, among other things, how much each person pays each week, versus how much they should’ve paid.

I use two linked tables to track this - one on which I record each individual transaction, and another that uses rollup fields to add each member’s transactions together so I can see each member’s history at a glance. I’ve set it up so that the Rollup table shows me how much (if anything) a member owes us in total, but the actual maths for that is done in the Transactions table.

At the moment, one food delivery costs £3, but we’re about to increase that to £4. My trouble is with how to get Airtable to reflect this change. If I just change the formula for the amount owed from {Packages delivered}*3 to {Packages delivered}*4 then it’ll re-calculate every member’s payment history and tell me that everyone is £1 per week in debt, so I’m hoping there’s an IF formula I can use to say “before 31.08.2020, it’s £3 per package; after 31.08.2020 it’s £4 per package”. I’ve tried everything I can think of, but I don’t have a good enough knowledge of formulas to make it work.

Thanks in advance for your help