Why the table freezes
The check arrives when everyone is tired, slightly buzzed, and nobody wants to look cheap. In that state, people round generously, split unevenly, and remember it with resentment. The fix is procedural, not moral: decide the method (even or proportional) and the tip before ordering, and the check becomes arithmetic instead of a negotiation.
The ambiguity tax
Unsettled group money — the "I'll get you back later" that never happens — functions as a slow tax on the group's goodwill. Studies of shared expenses keep finding the same pattern: ambiguity is not neutral, it systematically favors whoever ordered most and whoever follows up least. A calculator and a payment app that night eliminate the tax entirely.
Scripts that work
"18% on everything, even split — cool?" before the check lands. "Let me just run this" with the calculator already open. "I'll Venmo you tonight" instead of "I owe you one." None of these are awkward; ALL of them are cheaper than the resentment alternative. Fairness is mostly a timing problem.