Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

Shared groceries expenses between roommates to be divided as per specific consumption ratio and attendance
So your whole approach, and the attempt to scale this is flawed.  You will alienate roomates, provoke arguments, and make everyone's life more difficult.  There are too many variables and unforeseen possibilities.  For instance: "Why should I have to pay for Joe to go buy the expensive organic milk when I'm fine with the cheap stuff?" "I planned on being here for 20 days, but was gone that long weekend, recalculate everything please." "I already paid for this month, but now you're asking for more because James wanted to recalculate for a long weekend?" The right way to do this is to set up loose, reasonable agreement among the participants and treat that as a contract, but with some flexibility/mercy on small dollar amount items. For instance: There are 5 of us, so everyone provides food (and shops/cooks) one night a week.  We're solo on Friday and Saturday (people eat out more then anyway), and everyone puts in $10/week (or whatever) for breakfast cereal, snacks, etc.  If you can't be here on your night, work out to trade with someone.  If you miss out on a meal... oh well. As long as people feel like they have a say in the discussion generating this and it's not dictated to them, then most of the time this is far superior.  If people need this level of detail, then perhaps those people should live alone or move in with Sheldon Cooper from "The Big Bang Theory".