How to split bills when one of you earns more.

To split bills based on income: add both take home incomes, divide each person's income by that total to get their percentage, and apply those percentages to the shared costs. On 2,400 and 3,900 a month the shares are 38 and 62 percent, so 2,100 of shared bills comes out as 800 and 1,300.

That's the arithmetic, and it takes two minutes. The rest of this is the part that decides whether it survives a year: which of the three arrangements you're actually choosing, what each one does to the person earning less, and the four questions that break every one of them.

Two people share a flat. One takes home 2,400 a month, the other 3,900. Rent, bills, food and the standing charges nobody enjoys come to 2,100. The currency doesn't matter and neither does the exact rent. What matters is that there are only three sensible ways to divide that 2,100, they produce very different lives, and almost nobody sits down and picks one.

Splitting bills 50/50, and what it costs the lower earner

Straight halves. 1,050 each.

The person on 2,400 keeps 1,350. The person on 3,900 keeps 2,850. One of them has just over twice as much left as the other, from a gap in pay that was only about sixty percent.

That's the thing about splitting a fixed cost equally: it magnifies the difference in income rather than reflecting it. Shared costs are close to the same for both people, so they eat a much larger share of the smaller salary. The higher earner doesn't usually notice, because from where they sit the arrangement is obviously fair. Everyone paid the same.

Halves work when the incomes are close, or when both people would rather keep money entirely separate and are willing to pay for that with the arithmetic. They stop working the moment one person is saying no to things the other has stopped thinking about.

How to split bills based on income, step by step

Add the two incomes. 2,400 and 3,900 is 6,300. Work out each person's slice: 38 percent and 62 percent. Apply those to the shared 2,100.

• The person on 2,400 pays 800.
• The person on 3,900 pays 1,300.

Now the leftovers are 1,600 and 2,600, and the ratio between them is exactly the ratio between the salaries. Both people are spending the same third of their pay on the flat. Neither is subsidising the other in any sense that survives a conversation.

Two things to decide before this works in practice.

Which income figure. Use take home pay, after tax and after anything deducted at source. Gross pay flatters whoever has the bigger tax bill.

When it gets recalculated. Once a year, or whenever someone's pay changes by more than a little. Not every month, or the arithmetic becomes a monthly negotiation, which is the thing you were trying to avoid.

Equal leftovers: the version people arrive at when it is tight

Take the total income, 6,300. Take off the shared costs, 2,100. That leaves 4,200 of personal money, which is 2,100 each.

Work backwards. The person on 2,400 pays 300. The person on 3,900 pays 1,800.

This one is honest about what it's doing. It treats the household as one pot and gives both people the same spending money. It's common where one person earns much more, where one is studying or on parental leave, or where the gap is temporary and both of them know it.

It's also the arrangement most likely to be resented later, and usually not by the person you would guess. The higher earner is fine with it right up until something changes: a bonus that gets absorbed, a raise that produces no visible difference in their own life. If you pick this one, agree what happens to a raise before anyone gets one.

The three splits, side by side

Same flat, same bills, same month. Three arrangements, and the difference to the lower earner is 750 a month, which over a year is a holiday, or an emergency fund, or the deposit conversation happening a year earlier.

When one of you owns the home

The arithmetic above assumes the housing cost is a bill. If one of you owns the place, half of it is not: a mortgage payment is partly the cost of living somewhere and partly one person buying an asset the other will not own.

Splitting that in proportion to income means the non owner is paying towards somebody else's equity every month, which is fine if both of you have said so out loud and corrosive if only one of you has noticed.

What works is to separate the two. The non owner pays rent, set at something local and defensible rather than at half the mortgage. The owner covers the capital repayment, the buildings insurance and anything that is a repair rather than a bill. Everything else, energy, food, internet, council charges, goes through the ordinary split by income.

If the non owner ends up contributing more than a market rent, that's a conversation about ownership rather than about bills, and it's worth writing down while everybody is happy rather than reconstructing later.

Three people, or a couple and a flatmate

The percentages work exactly the same with three incomes, and the argument is never about the arithmetic. It's about the bedroom.

Two people sharing the largest room and one person in the small one is not three equal shares of the flat, whatever the incomes are. The version that holds is to divide the housing line by the space rather than by the head count, agree it once when someone moves in, and then apply the income percentages to everything else. A couple paying two thirds of the rent for the room that is two thirds of the flat is an arrangement nobody relitigates in March.

The parts that are not the split

Whichever you pick, four questions decide whether it survives contact with a real year.

What counts as shared. Rent, utilities, the internet, food eaten at home, cleaning, the boring insurance. Not clothes, not a phone contract someone chose, not a gym. Write the list down once. The arguments are almost never about the percentage. They're about whether a thing was on the list.

Savings. If you're saving for something joint, it goes in the shared column and gets split like everything else. If you are saving separately, it comes out of personal money and is nobody else's business. Mixing the two, where one person's saving is treated as a shared goal and the other's is treated as spending, is the fastest way to make one person feel supervised.

One offs. A washing machine, a flight for a funeral, a vet bill. Decide the threshold above which something is discussed rather than just paid for, and split anything above it the same way as everything else. A number that is unambiguous, like 200, beats a principle that is not.

Irregular income. If one of you freelances, the monthly percentage swings around and nobody wants to recalculate in February because January was quiet. Use a rolling average of the last three or six months, fixed for a quarter at a time. Being slightly wrong on purpose is better than being exactly right on a moving target.

The reason these splits fail is tedium

The arithmetic above takes two minutes. The work is everything after: someone pays the electricity, someone else buys the food, the numbers are on two different cards, and by the end of the month neither of you can reconstruct who owes what without going through statements.

That reconstruction job is the actual reason these arrangements fail. Not unfairness. Tedium.

What makes it stick is one place where shared spending lands as it happens, marked as shared, visible to both of you, with the rest of each person's money staying private. Then the monthly settle is a number you read rather than a number you build.

That's what shared money in Orla does. Accounts you choose to share, spending you mark as shared, a running balance of who is up and who is down, and one payment at the end of the month to flatten it. Everything you didn't share stays yours, including the accounts it sits in. If it's you and one other person, the couples and family side is the shape of it.

Pick badly, but pick out loud

The failure mode is not choosing the wrong one. It's never choosing, defaulting to halves because it needs no discussion, and finding out two years later that one of you has been quietly not going to things.