How to split expenses as a couple: by income, half and half, or something in between

Most couples never decide how to split shared costs. They fall into an arrangement in the first months and defend it for years. Here are the three arrangements, what each one assumes, and how to do the sums so the question is answered by a number rather than by whoever is more tired.

The three splits

• Half and half. Each partner pays 50% of shared costs. Simple, and fair only when incomes are close. With a large gap it leaves the lower earner with far less to live on after the joint bills.
• In proportion to income. Each partner pays the share of shared costs that matches their share of the household income. If one earns $6,000 and the other $3,400, the split of the joint costs is 64% and 36%. Both keep the same fraction of their own income.
• Everything pooled. All income into one pot, all costs out of it, personal spending drawn as an equal allowance. Cleanest when the pair see themselves as one economy; hardest when they do not.

None is right for everyone. What the research on money conflict shows is that the unresolved version, where the split is assumed and never stated, is the one that produces the arguments.

Which one couples actually live in

Incomes inside couples are more equal than they used to be but still rarely equal. Pew Research found that in 29% of U.S. marriages the spouses earn roughly the same, which means that in the other seven out of ten, half and half is a decision to tax the lower earner harder. A household with a $2,600 income gap is in the majority, and for that household the by-income split is usually where the sense of fairness lands.

Doing the sums

1. Decide what counts as shared: rent or mortgage, utilities, groceries, the children, the car, the joint subscriptions, and the savings transfer, which is the shared cost most couples forget to split. Everything else is personal.
2. Add up the shared costs for the month, whoever paid them.
3. Compute each partner's fair share: 50% each, or income share times the total.
4. Compare what each actually paid against their fair share. The difference is the settlement, and only one person owes it.

The rule that keeps this honest: a charge must belong to exactly one of three places, partner A, partner B, or the household. A grocery run on a personal card is still a household cost; a personal purchase on the joint card is still personal. Once every row has an owner, the settlement is arithmetic, not negotiation.

How PeakFinance does it

PeakFinance attributes every transaction to a member or the household, from the card that paid, a rule you taught it or the category's default owner. The “who spends what” screen shows each partner's personal spend, their share of the joint spend and their share of the month, and the settlement is computed under the split you chose, by income or half and half, with the direction and amount of the transfer stated. Change a single transaction's owner and the settlement moves with it.