Splitting household costs by income: how the math works

When two people in a home earn about the same, splitting everything in half feels fair. When one earns a lot more, half and half takes a bigger slice out of the lower earner's pay. A split by income asks each person to cover the same fraction of what they earn.

Households get stuck on the details: which incomes to use, what happens to personal purchases, and how a month of receipts turns into one payment.

From two incomes to two shares

A person's share is their income divided by the combined income of everyone in the split.

Say Sam earns $4,500 a month and Priya earns $5,500. Together that is $10,000. Sam's share is 4,500 out of 10,000, which is 45%. Priya's is 55%. Every shared dollar the household spends gets divided 45 and 55.

Pick the period before you do the arithmetic, monthly or yearly, and use the same one for both people. Do the same with the kind of figure, before tax or take-home. Only the ratio matters, so any consistent choice gives the same shares.

Setting it up in EvenHearth

Open the Household page. The split card has a Change the split button. In the dialog, choose By income and type each person's income. The percentage fields fill in as you type, in proportion, and you can adjust them by hand before you save.

The shares have to total exactly 100% before Save works. The incomes themselves are never saved. The dialog uses them as weights to produce the percentages, and only the percentages are sent.

A new split applies from the start of next month. Months already posted keep the split they were posted under, so a raise or a job change never rewrites last quarter.

What comes off before the split

Personal purchases leave the pile first. If Priya's hair dye sits on a receipt Sam paid for, it is Priya's alone, along with its own tax. Only the shared lines are divided 45/55. We covered that step in how to split a grocery receipt when one item is just yours.

One month, start to finish

Here is a month for Sam and Priya at 45/55. Everything listed is shared except the hair dye on the third entry.

Take the utilities row. 45% of $187.62 is $84.429, and nobody can pay a fraction of a cent. EvenHearth rounds to whole cents with a fixed rule, and the two parts always add up to the bill. Here Sam's part rounds up to $84.43 and Priya's rounds down to $103.19.

Add up the columns. Sam's parts come to $1,119.35 and Priya's to $1,384.36. Together that is $2,503.71, exactly what the household spent.

Who owes whom

A person's position for the month is what they paid minus what they owe. Sam paid $2,163.69, the rent plus the first grocery run, and owes $1,119.35, so the household owes him $1,044.34. Priya paid $340.02 and owes $1,384.36, so she is $1,044.34 short.

The two figures mirror each other. With two people they collapse into one payment: Priya sends Sam $1,044.34.

Settling up

Close the month in EvenHearth and it lists the transfers. For two people that is a single line. Priya pays Sam by whatever means they use, outside the app. Then Priya marks the transfer paid and Sam marks it received. Both confirmations are needed, so nobody can clear a debt alone, and the app never moves money.

With more than two people, the close lists a short set of transfers instead of one. The set never has more transfers than the number of people minus one.

Related reading

The split by income page covers the product side of this, and how it works follows a shared month from the first receipt to the last transfer. For how the Maliko Labs team ran the same job in a spreadsheet before building the app, see the spreadsheet we're replacing.