The bill you actually split most isn’t the dinner check
Split groceries with roommates by sorting one cart into two buckets: shared staples everyone uses (olive oil, dish soap, coffee filters) get divided evenly, and personal items (one person’s protein powder, someone’s specific brand of yogurt) get charged to whoever bought them. The even-split-everything shortcut feels fair for thirty seconds and quietly overcharges the light eater for months.
The dinner check is the bill people argue about. The grocery receipt is the one that comes back every week. Restaurants get the spotlight, but the shared household run repeats with the same people — same cart, same roommates, same quiet math. People are already splitting groceries. They’re mostly just splitting them badly.
A dinner gets split once and forgotten. Groceries are a recurring bill, and that’s exactly why the small unfairness matters: a $3 overcharge on one dinner is a rounding error, but the same $3 leak on a weekly grocery run is $156 a year flowing from the person who buys shared staples to the person who fills the cart with personal extras.