Picture the scene. You and your partner have just bought a place together. You’ve done the hard yards: saved the deposit, survived the auction, high-fived the conveyancer. Then the first mortgage statement arrives, and suddenly you’re having a very adult conversation about whether you really need to keep the heating on.
Welcome to homeownership in Australia in 2025.
Almost half of all Australian households with a mortgage are spending more than 30% of their disposable income on housing costs Australian Institute of Health and Welfare — the threshold that officially tips you into “mortgage stress” territory. In Sydney specifically, average monthly mortgage repayments now sit around $7,275, compared to $3,211 for rent Finder — a gap that makes your former rental feel like a bargain in hindsight.
So what do you do? You could refinance, cut the subscriptions, eat at home more. Or — and here’s the option more couples are choosing — you could just get a flatmate.
It’s not a new idea. It’s just an idea whose time has come back around.
This is not a new concept. Back in 2015, Domain was already reporting on married couples taking in housemates to help pay the mortgage — you can read that piece here. What’s changed is the scale of the problem. Average loan sizes have grown significantly, with the average mortgage in NSW now sitting at $828,000 — up $49k in a single year Wisebuy Home Loans. The couple in that 2015 story was dealing with a tough market. Today’s couples are dealing with a genuinely brutal one.
Which is why the spare room strategy is having a major moment.
The maths are hard to argue with.
There are an estimated 13.5 million spare bedrooms sitting empty across 10 million Australian homes, each potentially worth between $10,000 and $12,000 annually in rental income. Lifesherpa That’s not nothing. For a couple in Sydney carrying a $800,000 mortgage, even $250 a week from a flatmate could knock a meaningful chunk off the monthly repayments.
Some lenders have even started baking this into their calculations. CommBank, for example, is currently the only lender that allows eligible first-home buyers to include up to $150 per week from a flatmate in their loan assessment — effectively boosting your borrowing power before you’ve even moved in. CommBank
But wait, do I have to tell my lender?
Good news. If you have a mortgage, there’s generally no requirement to notify your lender that you’re renting out a room. Renting a room in your own home doesn’t mean you need an investment property loan Your Mortgage — a detail that surprises a lot of people. You will, however, want to look into the tax side of things, since rental income is generally assessable. Talk to your accountant.
Okay but what about, you know… us?
Fair question. You’ve built a life together. Now you’re voluntarily introducing a third person into it. Is this actually a good idea, or a very efficient way to create relationship friction?
Honestly? It depends entirely on how you set it up.
Sydney’s Emily, who shared a home with her now-husband and his best friend to cut costs, says the arrangement had real highs — and a few lows. The final straw came when she realised their flatmate was using the living room as his floordrobe. Her advice: “Make sure both your partner and your flatmate are house-trained.” CommBank
Solid advice. Here’s a bit more of it.
Talk to each other before you list the room. You and your partner need to be aligned before a stranger is. Whose friends are off-limits as candidates? What’s the quiet hours expectation? Is the flatmate included in the occasional Sunday dinner or strictly a separate household? Sort this out first, or you’ll be sorting it out at 11pm in a heated whisper.
Be honest in your listing. If you two are homebodies who like early nights and cooking elaborate meals together, don’t write “laid-back household, love a social flatmate.” You will get someone who invites people over on Wednesdays, and no one wins.
Set clear expectations upfront. Money, mess and privacy are the three biggest tension points in shared homes — a shared expense tracker or direct debit arrangement keeps bills fair, and early agreement on cleaning duties avoids the slow-burn resentment that tends to build around who last cleaned the bathroom. Your Mortgage
Consider a short-term lease first. A three- or six-month initial agreement gives everyone an exit ramp if the fit isn’t right. Much easier than an awkward conversation eighteen months in.
The right flatmate is actually a net positive.
Here’s the thing people don’t say enough: a good flatmate isn’t just a financial arrangement. They’re company. They’re someone who feeds the cat when you’re away. They’re an extra vote against the dodgy electrical work quote from the tradie your landlord — sorry, you — are now responsible for.
Done right, the flatmate-plus-couple configuration works. The financial logic is obvious. The social upside is underrated.
And given that in 2024–25, an estimated 1.26 million low-income households in Australia were in financial housing stress Australian Institute of Health and Welfare, finding creative ways to make the numbers work isn’t a sign of struggle. It’s a sign of sense.
Your spare room is sitting there. Your mortgage isn’t going anywhere. Might be time to introduce them.
Ready to find the right flatmate? Search for flatmates on flatmate.com — Australia’s original share accommodation platform.
