How to split trip expenses with a group without anyone keeping score

There are two ways money becomes a problem on a group trip. One is that nobody logs anything and on the last day you have to reconstruct five days of spending from memory. The other is that someone logs everything in painful detail and the group ends up debating whether the tip gets split evenly.

What follows is the middle ground, which is where this actually works.

Before you leave: agree on who logs, and where

You don't need a meeting. Two thirty-second agreements are enough:

One. Everybody logs their own expenses — not one person for the whole group. The classic mistake is appointing a "treasurer": that person ends up doing admin all trip, and on top of it they're the only one who knows how the tab is going. If each person logs what they pay, the balance is always current and nobody has to play accountant.

Two. One tool, chosen before you leave. It doesn't work if two people use an app, one uses their notes app and one plans to remember. The worst outcome is discovering on day 3 that there are two parallel lists.

During: log it right away, even roughly

An expense gets logged when it's paid. Not at the end of the day, not "when there's wifi". Ten seconds standing on the pavement is worth more than twenty minutes at night trying to remember what lunch cost.

And if you don't remember the exact amount, log the approximate one anyway. A $40 expense logged as $40 when it was really $38.60 introduces a 2% error. An expense that never got logged introduces a 100% error.

If you're logging four or five things a day, typing each one gets tedious fast; dictating them solves exactly that moment — the one where you're walking with your hands full.

The things not everyone used

This is where groups get stuck, and the rule that works is simple: split evenly by default, make an exception only when the amount justifies it.

• Dinner for six gets split evenly, even if one person ordered a starter. Arguing over $5 costs more than the $5.
• The excursion three of you did does NOT get split evenly. It's a big number and a real difference.
• Accommodation, if the rooms aren't equivalent, doesn't either. Split it by room.

The standard isn't perfect fairness: it's that the error from splitting evenly stays smaller than the cost of arguing about it. As the amount grows, that flips, and then itemising is worth it. The four ways to divide a cost — evenly, by percentage, by shares and by fixed amounts — and when to use each are laid out in shared expenses.

Currencies, if you're going abroad

A trip abroad adds the problem that half the expenses are in one currency and the group lives in another. Two rules:

1. Log each expense in the currency you paid it in. Converting in your head while travelling is the fastest way to end up with numbers that don't add up.
2. Lock the conversion to the day of the expense. If the app recalculates everything at today's rate, the trip changes size every time you open it and the balances between people stop being trustworthy. There's more on this in tracking two currencies.

When you get back: settle with as few transfers as possible

Six people who owe each other money don't need fifteen transfers. Once the debts are netted out, three or four almost always cover it: if you owe Juli and Juli owes Bruno, the right move is for you to pay Bruno directly.

The app does that netting for you. The only thing the group has to do is not leave it for two weeks, when nobody remembers anything and the money "stays for next time" — which is the polite way of saying someone paid more and isn't getting it back.

In one line

Everybody logs, log it in the moment, split evenly unless the amount justifies an exception, and settle as soon as you're back. The rest is bookkeeping nobody needs.

Kesef is free, on iPhone and Android

Shared expenses with no cap, 60+ currencies, and the numbers explained.