Group Trip Cost Splitter

Why the shortest settlement matters

Four people on a trip can easily produce a dozen shared expenses. Settle those one expense at a time and you get twenty small transfers, most of which cancel each other out. Settle on net balances instead and four people never need more than three transfers, however many receipts there were. In general a group of n people can always be settled in at most n − 1 payments, because each transfer can zero out at least one person.

The method here is the obvious greedy one: work out what each person is owed or owes overall, then repeatedly take the largest creditor and the largest debtor and move as much as possible between them. That clears at least one person from the list every time, so it terminates quickly and in practice hits the minimum. Finding the provably smallest set of transfers in every case is a hard problem — it is equivalent to partitioning the balances into subsets that each sum to zero — but the greedy answer is as good on real trips, and it is the one you can check by hand.

The cases that break simpler splitters

• Expenses only some people shared. Two people took the museum, four ate dinner, three were in the car for the petrol. Dividing everything by the group size is wrong and produces exactly the resentment the splitter was meant to avoid. Name the sharers per line.
• Someone who paid for nothing. Perfectly normal, and it simply means they end up owing. A person can appear in the sharer lists and never in the payer column.
• Someone who shared nothing. Also normal — they joined for two days, or they are settling separately. If a name never appears as a sharer, their balance is whatever they paid, and the group owes it back.
• Uneven shares. One person covering a partner or a child is not an equal share. Ani*2 in the sharer list counts Ani as two people for that expense only.
• Rounding. Splitting 100 three ways gives 33.33 each and loses a cent. This page works in whole cents and puts the odd cent on the largest balance, so the transfers always sum exactly to zero. A splitter that rounds each share independently leaves a few cents floating and looks broken.

Get the currency right before you start

This page does no conversion, and mixing currencies in the list produces a confident, wrong answer. If the trip crossed a border, convert everything to one currency first, at the rate you actually got — for card payments that is on your statement, and it is not the mid-market rate you will find quoted online. Then paste the converted figures here.

A convention that prevents most arguments

Agree at the start of the trip on what counts as shared. Drinks after dinner, the taxi one person took because they were tired, the ticket someone bought and could not use. None of these are difficult once decided in advance, and all of them are difficult decided afterwards with a spreadsheet open. The other half of the same convention: write the expense down the day it happens, with who was there. Reconstructing week two from memory is where the money actually goes missing.