You don't need a system. You need one formula you can redo in two minutes whenever something changes. This is that formula.
Want the numbers instantly? Use our free bill split calculator to compare an income-based split with 50/50 in euros.
The method in one line
Your share of the bills = (your take-home ÷ combined take-home) × total shared bills
That's the whole method. Everything else is just being consistent about which numbers you feed it.
- Take-home means net pay, after tax.
- Shared bills means costs you both rely on — housing, utilities, internet, groceries, joint insurance, shared transport.
- Personal spending stays out. Phones, hobbies, clothes, individual subscriptions.
A worked example
Two people take home €2,800 and €1,700. Their shared bills for the month come to €1,800.
| Person | Take-home | Share of income | Pays | % of their income |
|---|---|---|---|---|
| Partner A | €2,800 | 62% | €1,116 | 40% |
| Partner B | €1,700 | 38% | €684 | 40% |
| Total | €4,500 | 100% | €1,800 | — |
Notice the last column: both people end up under the same amount of pressure. That's the entire point of the method. Under a 50/50 split they'd each pay €900 — 32% of one income and 53% of the other.
Use take-home pay, not gross
Gross salary is the wrong input. Two people on the same gross can take home noticeably different amounts once tax bands, pension contributions and local deductions land. The bills are paid out of net income, so net income is what sets the shares.
If your income is variable — freelance, commission, seasonal — average the last six months of post-tax income and treat that as your figure. Re-average twice a year rather than fiddling monthly.
Keeping it fair as things change
The percentages are a snapshot. Three things keep the snapshot current:
- A quarterly ten-minute review. Both incomes on the table, redo the formula. Calendar it so it isn't anyone's job to bring it up.
- An automatic trigger. Any income change over 10% means you recalculate now, not at the review.
- A visible record. Percentages don't help if neither of you can see who actually paid what. Without a shared ledger both partners tend to overestimate their own contribution, and the formula gets blamed for a bookkeeping problem.
Two variations worth knowing
Proportional on big bills, even on small ones. Split rent and utilities by income, split groceries and small joint spending down the middle. Less arithmetic, nearly the same outcome.
Deduct fixed debt first. If one person carries a large loan payment, some households subtract fixed debt payments from each income before calculating shares. Reasonable — as long as it's an explicit agreement, not a quiet assumption.
Frequently asked questions
How often should the percentages change?
Only when income does. Most couples update two to four times a year.
Does the higher earner get more say over spending?
No. Paying a bigger share reflects earning more; decisions stay equal. Say that out loud once and it stops being a question.
What if the gap is enormous?
The formula still holds, but check the result against reality — the lower earner should end up with enough left to save something. If they don't, the shared budget is too high, not the split.
Can we use this with separate bank accounts?
Yes. Either pay your share into a joint account each payday, or each pay certain bills and settle the difference once a month.
Skip the spreadsheet
SharedNest stores both incomes, applies the percentage to every shared expense as you log it, and keeps one running balance so you always know who owes what. Start free while we're building.
