How to split expenses as a couple

Couples rarely fight about the maths of splitting expenses. They fight about the feeling that one of them is carrying more, which grows quietly when nobody wrote anything down. The fix is to pick a rule, apply it to a list you both agree on, and look at the numbers once a month instead of every day.

50/50 or proportional to income?

These are the two methods that hold up. Everything else is a variation.

50/50. Every shared cost is halved. It is simple, it needs no conversation about salaries, and it feels clean. It works well when your incomes are roughly similar — say, within 20% of each other — or when you are early in a relationship and not yet sharing much beyond dinners and the odd weekend away.

Proportional to income. Each of you pays the same percentage of your income towards shared costs, so the person who earns more pays more in absolute terms. It is the fairer choice when incomes are far apart, because an equal split would leave one partner with plenty of spending money and the other with almost none.

A quick test: work out what each of you has left each month after paying your half. If one person is left with a comfortable cushion and the other with nothing, 50/50 is not working, however tidy it looks.

There is no third option where you “just see how it goes”. That is how one person ends up paying for every grocery run for a year without either of you noticing until it comes up in an argument about something else.

How to split proportionally: a worked example

Ana takes home €3,000 a month and Ben €2,000. Together that is €5,000, so Ana’s part is 60% and Ben’s is 40% — a ratio of 3 to 2.

In one month their shared costs were:

Each row is split 3 to 2: €471.35 × 3/5 is exactly €282.81, and the remaining €188.54 is Ben’s. Check any row — the two parts add back to the total.

Ana paid €1,400.00 but her part is €1,200.00, so she is €200.00 ahead. Ben paid €600.00 against a part of €800.00, so he is €200.00 behind. One transfer settles the month:

Compare 50/50: each would have paid €1,000. That is a third of Ana’s income and half of Ben’s. The proportional split costs each of them 40% of what they take home — the same burden, different amounts.

You don’t need to compute every row by hand. Enter each expense split by shares — 3 for Ana, 2 for Ben — and the parts work themselves out. In kisir that is the Shares split; if your ratio is less tidy than 3 to 2, enter the exact amounts instead.

To try your own numbers first, the split bills by income calculator shows each person’s part next to what 50/50 would be.

When one pays the rent and the other pays groceries

This is the most common arrangement and the one most likely to drift. It starts as “you pay the rent, I’ll cover food” and feels roughly even. Then rent goes up, or one of you starts buying the expensive coffee, and nobody re-checks.

The ratio does not have to match the bills. Ana paying rent and Ben paying groceries is fine — the monthly settlement corrects the difference. What matters is that both of you log what you pay, so the correction is based on numbers rather than impressions. “I think it’s about even” is how one person ends up €150 a month out of pocket for a year.

Joint account or tracking?

A joint account works if you both pay in the agreed ratio — €1,200 and €800 in the example — and every shared cost comes out of it. It removes the monthly settlement entirely. The weak points: someone pays a shared bill from a personal card in a hurry, or the account runs low and one person tops it up without the other matching.

Tracking keeps your money separate. Each of you pays shared costs from your own account, logs them, and you settle once a month. It suits couples who are not ready to merge finances, who live together but keep separate lives, or who simply prefer it.

Plenty of couples do both: a joint account for the fixed bills and a shared log for everything else. The one thing to avoid is a joint account that is “mostly” used, with a stream of side payments nobody records.

What counts as shared?

Write the list once, together. A typical one:

• Shared: rent or mortgage, utilities, internet, groceries for the household, cleaning supplies, meals out together, holidays together, a shared car.
• Personal: clothes, hobbies, your own phone bill, gym, gifts from you alone, lunches at work.
• Decide explicitly: pets, furniture (who keeps it if you split up?), gifts to each other’s families, a subscription only one of you uses much.

The grey zone is where arguments live, so don’t leave it grey. If you can’t agree, split those items 50/50 regardless of the main rule — a simple compromise that ends the discussion.

Keeping it unemotional

Money talk between partners gets heated because it sounds like a judgement on effort or character. A few habits take the heat out:

• Settle on a schedule. The first Sunday of the month, the day after payday — any fixed date. A routine settlement is admin; a settlement because someone finally said something is a confrontation.
• Look at the total, not each item. Reviewing every grocery receipt turns a partner into an auditor. Check that the list is followed and the monthly number makes sense.
• Revisit the ratio, not the rule. When someone gets a raise, changes job or goes part-time, recalculate the percentages. The method stays; the numbers move.
• Leave room for generosity. A ledger does not stop either of you from treating the other to dinner. Just log it as personal, so the shared account stays honest.

When income changes because of parental leave, illness or study, many couples move from proportional to “one of us covers more for now” on purpose. That is fine — it is still a rule, agreed out loud, rather than something that just happened.

Keep a record you can both see

A shared log both of you can open — a spreadsheet, a note, or an app — means neither of you has to remember or defend a number. If you use kisir, you can both join a group by link or code with no account, add expenses as they happen, and export the ledger to Excel whenever you want to look back over a year.