Why we're building Kin

Most money apps for groups ask one question: who paid, and how do we split it evenly? That works for a dinner with friends. It works less well when you live with someone, and it breaks down when the people sharing a home earn very different amounts.

If one partner earns $90,000 and the other earns $45,000, an even split of a $2,400 rent takes the same $1,200 from both. For one of them, that’s a much bigger slice of their paycheck. Nobody planned for it to be unfair. It’s just what the default does.

Kin is a money app for couples, polycules and roommates that starts from a different default: shared costs are split by what each person can afford, not down the middle.

Fair isn’t always equal

This isn’t a new idea. A lot of people who give money advice to couples land on it. Ramit Sethi, in Money for Couples, tells partners to split shared costs in proportion to income: if you earn 75% of the household’s income, you pay 75% of the shared bills. Financial therapists make a similar point, that a strict 50/50 split ignores real differences in income and background, and that each couple should decide together what “fair” means to them.

The research behind this is worth knowing. In a study of more than 4,500 couples, disagreements about money were the strongest predictor of divorce among the types of disagreement it measured. What drove those fights wasn’t how much money a couple had. It was whether one partner felt the arrangement was unfair (Dew, Britt and Huston, 2012).

So the problem isn’t really arithmetic. It’s that the default split quietly decides what’s fair for you, and that can build resentment nobody talks about.

Keeping score has a cost

Here’s the part that surprised us. Psychologists distinguish between exchange relationships, where people expect to be paid back item by item, and communal relationships, where people look after each other’s needs without tallying. Studies have long found that keeping careful score tends to feel bad in close relationships, even though it’s perfectly normal between roommates or acquaintances.

A two-year experiment with engaged and newly married couples points the same way. Couples who were asked to merge their money into a joint account kept their relationship quality high, while couples who kept separate accounts showed the usual decline (Olson and colleagues, 2023). The couples with separate money drifted toward “I’ll pay you back” thinking.

That’s a problem for apps built around itemized IOUs. Logging every coffee and toilet roll and settling up each one is exactly the score-keeping that wears on partners. It’s also exactly what roommates need.

So Kin is being designed with two ways of working:

• A shared pot, for couples and polycules. You agree on a fair-share ratio once, each person contributes their share to the pot, and shared spending comes out of it without anyone tallying who bought what.
• A ledger, for roommates and other more transactional households. Every shared cost is itemized and split, with a clear “who owes whom” at the end of the month.

Both use the same fair-share ratio underneath, so you can split by income, by room size, or by whatever your household agrees on.

Built for more than two

Most finance apps assume a household is one or two people. Plenty of households aren’t. A polycule might share rent between three people, groceries between two of them, and a holiday between four. A roommate house might share utilities equally but split rent by room.

Kin is being built around overlapping groups, so each cost belongs to the people it actually belongs to, each with its own split. One person can be part of several of these at once and still see one clear picture of what they owe and are owed.

Your money stays yours

Sharing finances shouldn’t mean sharing everything. When you link a bank account to Kin, nothing is shown to anyone by default. You choose which transactions are shared, and your personal spending stays private.

Kin also won’t hold or move your money. It tracks shared costs and works out who owes whom. When it’s time to even up, you pay each other with the apps you already use, like Venmo, Zelle or Cash App.

Where we are

Kin is in early development. The first version will be a small test with friends and family in the US, and we’ll be writing here about what we learn along the way, including what the research says about money and relationships, how different households split costs, and what we get wrong.

If any of this sounds like your household, join the waitlist. We’ll send occasional updates about Kin’s progress and let you know when you can try it.