How to split bills with your partner: 3 fair methods

Before you choose: what gets split

All three methods start from the same question: which costs are shared? Usually rent or mortgage, utilities, groceries, meals out together, and trips. Personal spending stays out: clothes, the gym, hobbies, gifts for each other.

For the example, take a couple with take-home pay of $5,000 and $3,500 a month, and $2,720 of shared costs: $1,600 rent, $720 groceries, $400 utilities.

Method 1: fifty-fifty

Each of you puts in half of the shared costs, $1,360.

• The partner earning $5,000 keeps $3,640.
• The partner earning $3,500 keeps $2,140.

It's the easiest to run: every cost gets divided by two. With similar incomes it's also the fairest. As the gap grows, the lower earner ends up putting a much bigger slice of their pay into the household: here 39%, against 27% for the other partner.

Method 2: in proportion to income

Each of you pays according to your share of the total income. Together you take home $8,500: $5,000 is about 59% and $3,500 about 41%. Of the shared costs, one of you puts in $1,600 and the other $1,120.

• The partner earning $5,000 keeps $3,400.
• The partner earning $3,500 keeps $2,380.

Now you both put the same slice of your pay into the household, 32%. Many couples find this the fairest option when incomes are far apart. The cost is one more calculation each time, which the split bills by income calculator does in a minute.

There's also a variant, for couples who want to keep the same amount each: subtract the shared costs from your combined pay and split what's left. Here $8,500 minus $2,720 is $5,780, so $2,890 each: one of you puts in $2,110 and the other $610. It's the most generous split for the lower earner, so talk it through before choosing it.

Method 3: by bill

Each of you takes over certain fixed costs: one pays rent, $1,600; the other covers groceries and utilities, $1,120. Those happen to match the income split, and for a while it works without any math.

The trouble comes over the months. In January, utilities go from $400 to $560, and whoever pays them is now putting in $1,280 instead of $1,120. In August groceries drop because you're away, but who's paying for the trip? After a few months neither of you knows if the split is still fair. So even when you split by bill, it's worth logging costs and checking the balance now and then.

How to keep track, whatever method you pick

The method matters less than you'd think: what causes arguments is not knowing where you stand. There are three ways to keep track:

• a joint account that each of you pays your share into, and that household bills come out of (read the pros and cons of a joint bank account first);
• a spreadsheet, which works as long as someone keeps it up to date;
• an expense sharing app for couples, where you log costs as you pay and the balance updates on its own, using the split you chose. Here's a comparison of expense sharing apps.

Which one to choose

• Similar incomes, less than about 20% apart: fifty-fifty.
• Incomes far apart: by income, or the variant if you want to keep the same amount each.
• Very steady bills and little appetite for math: by bill, checking the balance every few months.

You can change methods: if one of you changes jobs or goes on parental leave, redo the math together. And if you're married in Italy, your property regime decides who owns your savings, not how you split bills; we explain it in community or separate property in Italy. More guides are in splitting costs.