How to Split Living Costs with a Partner or Roommate: Deciding Shares of Rent and Utilities

There are three main ways to split

You can invent endless variations, but the ones that actually last are one of these three. None of them is the right answer; choose based on how big the income gap is and how unevenly the housework falls.

• Dividing by expense means little settling up, but whoever pays the rent tends to pay far more than the other. Look at the amounts before assigning them.
• Splitting by income can feel “fair but restrictive”. Rounding to something like 60/40 or 70/30 rather than an exact ratio makes it easier to run.
• Even if you decide on 50/50, if the housework is lopsided you’ll need to balance it some other way. Don’t try to settle fairness through money alone.
• Whatever the method, write down what you agree. Verbal agreements drift apart in memory within a few months.

What counts as a shared cost

Before deciding the shares, decide what you’re sharing. If this stays vague, every month brings a negotiation over whether something is shared or personal. For anything borderline, the quickest way is to list it and sort it in advance.

Electricity doesn’t double when the household doubles: in Japan a single-person household averages around ¥7,600 a month and a two-person household around ¥11,100. You can get an idea of what utilities might cost when two of you move in together from average electricity bills.

Calculating shares by income

1. 1

   Bring your take-home pay

   Use take-home pay after tax and social insurance, not gross pay. Calculating from gross pay skews the ratio away from what you can actually spend because of differences in deductions. If you get bonuses, average them out by dividing the annual total by 12. If you don’t have payslips to hand, you can estimate it from annual income with how to calculate take-home pay.

2. 2

   Work out each share of the total

   If your take-home pay is ¥280,000 and ¥200,000, the total is ¥480,000 and the ratio is about 58 to 42. You don’t need decimals; round it to something easy to handle, such as 60/40 or 58/42.

3. 3

   Fix the total of shared costs

   Add up all the shared costs for the month. Fixed costs are the same every month, so you only need to total the variable ones.

4. 4

   Split by the ratio

   In the Bill Splitter’s Custom split, choose “Split by ratio” and enter the total and each person’s share. The ratio fields are calculated relative to their sum, so 58 and 42 give the same result as 6 and 4.

5. 5

   Decide how to handle remainders

   You can choose to round up, to the nearest or down. Any remainder is adjusted automatically on the first person, so the total collected always matches.

Splitting by income means the higher earner pays more in money terms, but the proportion of take-home pay left over is the same for both. Equalizing the proportion left rather than the amount left is the whole point of splitting by income. If buying a home comes up later, calculating how much you can borrow, which also starts from take-home pay, is a useful reference.

A system that keeps monthly settling-up from piling up

Even with a method agreed, one person often does the actual paying, and advances pile up. Deciding how you’ll settle up in advance means no more going through receipts at the end of the month. To reflect an income gap in the shares, see how to decide who pays more; for one-off advances such as on a trip, see how to split travel costs.

1. 1

   Record what was paid

   Just note who paid how much in a shared note or budgeting app. Detailed categories can wait.

2. 2

   Run the settle-up calculation at month end

   In the Bill Splitter’s Settle up tab, enter each person’s name and the total they paid. It shows who should give how much to whom in the fewest transfers.

3. 3

   If shares aren’t equal, adjust with the difference

   The Settle up tab calculates differences assuming equal shares. If you split by income, first work out each person’s share with Custom split, then send the difference.

4. 4

   Always settle on the same day

   Allow “let’s just do this month with next month’s” once and the amounts balloon and get harder to settle. Fixing a date, such as payday, is the trick to keeping it going.

Ground rules to avoid arguments

• Review once a year, and whenever someone changes jobs, moves or changes how they work. Adjusting every month means the negotiating never ends.
• Decide how to share the housework at the same time. Even if the money is equal, resentment remains if the time burden is lopsided. Writing down how long things take and comparing helps the conversation along.
• For expensive furniture and appliances, decide when you buy them what happens if you split up. For things bought 50/50, keeping it to two options (one buys the other out, or you sell and split) makes it simple.
• With a joint account, the person whose name it isn’t in may be limited in closing it or withdrawing money. Check at the start whose name it’ll be in and how the balance will be handled.
• Decide whether to pool savings separately from living costs. Mixing day-to-day costs with saving for the future turns every settle-up into a big discussion.

FAQ

Should a couple living together split costs 50/50 or by income?

If your take-home pay differs by less than 20%, a 50/50 split rarely causes strain; beyond that, splitting by income is more realistic. Splitting by income means you pay different amounts but keep the same proportion of your take-home pay. If you’re unsure, calculate how much the lower earner would have left under a 50/50 split. If it isn’t enough to live on, that’s a reason to split by income.

Where should the line between shared and personal costs be?

The basic rule is that things both of you use equally are shared, and things for one person are personal. Rent, utilities, internet, groceries and household goods are shared; clothes, cosmetics, hobbies and socializing are personal. The borderline cases are alcohol only one drinks, takeout and food for guests. Settle those three in advance and the monthly negotiations disappear.

How do I calculate settling up when advances have piled up?

Enter the total each person paid, and you get who should give how much to whom in the fewest transfers. In flatshares of three or more, having everyone pay everyone means lots of transfers, so this method is especially useful. If shares aren’t equal, first work out each person’s share by ratio, then find the difference.

How often should we review the shares?

Review once a year as a matter of routine, and also when someone changes jobs, gets a raise, moves or changes how they work. Adjusting every month means constant negotiating and defeats the point of setting shares. Fixing a review date in advance and not touching the shares on any other day makes it easier to run.