Expense Splitter — settle up with the fewest transfers

The naive way to settle a group trip is for everyone to pay everyone else back directly, which on six people can mean fifteen separate transfers. Most of those cancel out. If Ana owes Bo $20 and Bo owes Cy $20, Ana can simply pay Cy and Bo does nothing.

This tool nets everyone's position first, then matches the largest debtor to the largest creditor repeatedly. That never needs more than one transfer fewer than the number of people, and usually far fewer. Finding the provably smallest set is a hard problem in general, but this greedy match is optimal for realistic group expenses.

The other half of the job is cents. Split $100 three ways and you get $33.33 each, which is $99.99 — a cent short. Tools that work in floating-point dollars leave that penny floating around as a debt that never quite settles. This one works in whole cents and hands the remainder to specific people, so the balances always sum to exactly zero.

Uneven sharing is the common case, not the exception. One person skips the taxi, two share a hotel room, someone leaves early. Each expense here carries its own list of who it applies to, so the split reflects what actually happened rather than dividing everything equally.