When you live together, sooner or later the question comes up: how do we split the expenses? The automatic answer is "fifty-fifty". It sounds fair, but it only really is when you earn similar amounts. When one income is much higher than the other, 50/50 becomes quietly unfair.

The problem with "fifty-fifty"

Picture a couple: one earns €2,400 a month, the other €1,200. The rent is €900. Split in half, each puts in €450. But for the person earning €1,200 that €450 is 37.5% of their income; for the one earning €2,400 it's just 18.75%. The same amount "weighs" twice as much on one person. The result: whoever earns less is left short of breath, while the higher earner has plenty of room. It isn't unkindness — it's just badly set-up arithmetic.

Splitting in proportion to income

The fair alternative is to split shared expenses in proportion to what each person earns. You add the two incomes, work out each person's percentage share, and split every shared expense using those percentages.

Back to the example: total income €3,600 (2,400 + 1,200). The person earning 2,400 contributes 66.7%, the one earning 1,200 contributes 33.3%. On €900 of rent that means €600 for the first and €300 for the second. Now the effort is the same for both: each sets aside the same percentage of their own income.

Shared expenses, yes — but not everything is shared

Proportional doesn't mean "pool everything". It works best if you separate two kinds of spending:

  • Shared expenses — rent/mortgage, bills, groceries, the home: split proportionally.
  • Personal expenses — your subscriptions, your hobbies, the gifts you give: stay with whoever spends them.

That way you keep fairness on the shared accounts and independence on personal choices, without having to justify every little purchase to the other.

What about "settling up" at the end of the month?

Many couple-expense apps think in terms of "who paid for what" and settle up at month end: one person owes the other money. That's more of a roommate model than a couple model. A calmer alternative is to share without settling up: you decide each person's share, everyone puts in their part, and nobody "owes" anyone. Less accounting, less tension.

In practice, every month

  1. Note both net incomes.
  2. Work out each person's percentage share.
  3. Apply those percentages to every shared expense.
  4. Leave personal expenses with whoever makes them.

You can do it by hand with a spreadsheet, but it gets tedious to keep updated. That's exactly the calculation TogetherExpenses does automatically: enter your incomes once, add your expenses, and the app shows each person's fair share in real time — shared and personal kept separate, with no settling up.