Splitting expenses by income as a couple: calculator and formula
Proportional expense calculator
Enter what each of you earns and how much you spent together this month. It tells you how much each person should put in according to their income and, if you like, who owes whom.
- Your share
- 2,700 60%
- Your partner's share
- 1,800 40%
That way you both put in 45% of what you earn.
Splitting fifty-fifty, you'd put in 37.5% of your income and your partner 56.3% of theirs.
If one of you earns a lot more, splitting everything down the middle leaves one person comfortable and the other scraping by. A proportional split fixes that: each of you puts in the same percentage of what you earn. The calculator above does the maths; below are the formula, an example and the questions that come up once you put it into practice.
The formula
Each person's share is their income divided by the two incomes added together. That percentage is applied to the shared expenses.
- Your share = your income ÷ (your income + your partner's)
- What you put in = shared expenses × your share
An example with numbers
One of you earns 6,000 and the other 4,000: 10,000 together. The first person's share is 60% and the second's is 40%. If this month's shared expenses add up to 4,500, one puts in 2,700 and the other 1,800.
That way you both contribute 45% of your income. Splitting fifty-fifty, on the other hand, you'd each put in 2,250: that's 37.5% of what the first person earns and 56.3% for the second. The gap between "we paid the same" and "it cost us the same" is exactly that.
Which income counts?
- Net, not gross. What each of you takes home after deductions and tax: that's the money actually available.
- Variable income, averaged. If one of you earns commission or works project by project, use the average of the last three to six months rather than recalculating every month.
- Bonuses, kept separate. It's better to leave them out of the monthly sum and decide together what to do with them.
Which expenses go into the split?
The ones that belong to both of you: rent, bills, groceries, internet, things for the home. Personal spending —each person's clothes, nights out, subscriptions— comes out of what each of you has left. If you don't agree on this up front, every borderline expense turns into an argument.
When to recalculate
The percentage has to move when your incomes move: a pay rise, a new job, time off. With inflation, salaries get adjusted several times a year, and a percentage worked out in January can be way off by June. A simple rule: revisit it whenever either of you gets a raise.
What the formula doesn't solve: who paid for what
Knowing your share is 60% doesn't help much if expenses were paid by whoever had their card handy. At the end of the month you compare what each person put in with what their share was, and settle the difference with a single transfer. That's what the calculator's last field is for: enter how much you paid and it tells you who transfers to whom.
That sum only works if every expense was written down. On Expenses you both log what you pay in a shared space, and the list shows who logged each expense and the month's total: the numbers for the calculator are right there, with nothing to piece together from memory. If you haven't picked a method yet, we compare the four most common ones in how to split expenses as a couple.