What "fair" means once incomes differ
Two couples can split the same €2,600 of shared costs identically and end up with completely different levels of stress. That is because there are two definitions of fair hiding inside the word: everyone pays the same amount, or everyone pays the same proportion of what they earn. When incomes are close, the two definitions agree. When they diverge, you have to choose.
The 50/50 split: equal amounts, unequal pain
Each partner pays half of every shared cost. It is the easiest rule to state, it needs no calculation, and it treats both partners as equals by construction.
The problem shows up in what is left over. An equal payment is a much bigger bite out of a smaller income, so the lower earner ends up with far less personal money than the higher earner. Nothing about the arrangement looks unfair on paper — the imbalance only appears once you look past the transfer and at the remainder.
The proportional split: equal share of income
Each partner pays a share of the shared costs equal to their share of the combined income. Someone earning 70 % of the household income covers 70 % of the bills.
The rule is slightly harder to state and needs recalculating when a salary changes, but it produces something the equal split cannot: both partners hand over the same share of what they earn, and both keep the same share for themselves.
The same numbers, both ways
Take incomes of €4,200 and €1,800 a month, with €2,600 of shared costs.
Split equally, each pays €1,300. That is 31 % of the higher income and 72 % of the lower one. The higher earner keeps €2,900 for personal spending; the lower earner keeps €500.
Split proportionally, the higher earner pays €1,820 and the lower earner €780. Both now spend 43 % of their income on the household. The higher earner keeps €2,380 and the lower earner keeps €1,020 — roughly double, with no extra euro entering the household.
The household total never changed. Only the definition of fair did.
The third method: "you take X, I take Y"
Plenty of couples never split individual bills at all. One partner covers rent, the other covers groceries, utilities and insurance. It is low-friction and needs no monthly maths.
It works when the two bundles happen to land near the split you would have chosen anyway. It quietly fails when they drift — rent rises faster than groceries, and the person holding rent is absorbing an increase nobody agreed to. If you use this method, re-check the totals once a year and rebalance which bills sit on which side.
The three methods side by side
| Method | Effort | Handles unequal incomes | Fails when |
|---|---|---|---|
| Equal (50/50) | None | No | Incomes diverge |
| Proportional | Recalculate on a raise | Yes | Incomes are hard to pin down |
| Category ("you take X") | None after setup | By accident only | Bill sizes drift apart |
Protect a personal-money floor
Proportional splitting can still squeeze someone if the household is expensive relative to both incomes. The fix is to agree a personal-money floor — a minimum each partner keeps whatever the split says — and to treat any shortfall as a household problem to solve, not as one partner's failure. Cut a shared cost, change the split temporarily, or draw on savings, but decide it together.
Where the equal split still wins
If your incomes are within roughly 10–20 % of each other, split equally. The proportional version buys you almost nothing and costs you a recalculation every time either salary moves. Simplicity is worth real money in a rule you have to follow every month for years.
Set your own split
The couple budget planner takes both incomes and your shared costs and shows the equal split, the proportional split, and what each partner is left with under each. Run it once, agree the number, set up the standing transfer.
Where the money should live
Once you know the amounts, decide which accounts they move through — joint, separate or hybrid changes how much administration the split costs you every month.