How Cost-Sharing Works in Kai: Two Questions, Not One

Most groups think of cost-sharing as a single setting: "how do we split the costs?" In practice it is two separate questions, and keeping them apart is what makes a shared aircraft, yacht, vehicle, or property feel fair instead of fiddly.

1. When a cost is shared, how is it divided between members?
2. For any given expense, is it shared at all, or does one person carry it?

Kai treats these as two different controls. Get both right and everyone's balance moves the way they expect after each expense.

Question 1: how a shared cost is divided

This is the group-wide split method. You set it once, under Group settings, Financial, Expense sharing (or quickly on the new Essentials page). It decides how any shared cost is spread across members:

• Equal. Evenly across all active members. A €200 fuel bill among four members is €50 each.
• Proportional to ownership. By each member's ownership percentage, or by share count if your group is share-based. If A holds 40% and B and C hold 30% each, a €1,000 cost becomes €400, €300, and €300.
• None (manual). No automatic split. You record each member's share by hand when you want full control.

That is the whole of question 1. It is a property of the group, not of any single expense.

Question 2: whether an expense is shared

Here is the part groups miss. Not every cost should be split. Fuel you burned on your own trip is yours. A new set of sails is everyone's. So Kai decides sharing per expense, and how that works depends on whether your group uses invoicing.

• Invoicing groups. A member-paid expense defaults to reimbursing the payer in full. Nothing is split, and you get your money back. If the cost really is shared, you turn on "Split cost among members" on that expense, and it splits using the group method from question 1.
• Non-invoicing groups. Every expense is split among members automatically. There is no per-expense opt-out. If you want the "keep it on the payer" option, turn on invoicing (Essentials, Money, Invoicing).
• Paid by the group. For costs paid straight from the shared group account, no one is reimbursed, but members still owe their share to the group.

The default matters: in an invoicing group, adding an expense does not quietly bill everyone. It pays you back. Splitting is the deliberate choice.

A worked example

Say you hold 2 shares, three other owners hold 10 each, and the group uses invoicing with Proportional to ownership.

• You buy €120 of fuel for your own voyage. Leave "Split cost among members" off. It stays entirely yours.
• The group replaces a €3,200 sail. Turn "Split cost among members" on. It splits by shares: your part is about €200 (2 of 32 shares) and each 10-share owner pays about €1,000.

Same group, same split method, two very different outcomes, because question 2 was answered differently for each expense.

Where each one lives

• Split method (question 1): Group settings, Financial, Expense sharing, or the Essentials page under Money.
• Split vs reimburse (question 2): the "Split cost among members" toggle on the expense form, in invoicing groups.

The short version

Set your split method once. Then, for each expense, decide whether it is shared. Personal costs stay with the person who paid; genuinely shared costs get split the way your group agreed. Two questions, answered in two places, and nobody is surprised by their balance at the end of the month.

Want to see it on your own numbers? Demo at kai-sharing.com.