Buying a duplex means you're taking on two properties at once, which changes how lenders look at your application.
A duplex on one title gets treated as a single security, but most lenders will assess rental income from both dwellings separately and apply serviceability buffers to the full loan amount. That affects how much you can borrow and which lenders will take the deal. The federal tax changes that came through in June have also shifted the way new duplex purchases stack up financially, particularly if you're buying established stock versus new builds.
How lenders assess a duplex investment loan
Lenders assess a duplex as one property with two income streams. Each dwelling's rental income gets discounted, usually by 20 to 30 per cent, to account for vacancy and maintenance. The full loan amount then goes through the serviceability buffer, which adds three percentage points to the product rate. That's been the case since mid-2025 and it tightens things up compared to a few years back.
In our experience, buyers in Shelly Beach looking at older duplexes near the foreshore often find that one unit rents for more than the other because of ocean glimpses or a larger layout. Lenders will take both rents into account, but the gap matters when you're trying to show enough income to cover repayments. If the duplex is on the older side and one unit is dated, the rental appraisal might come in lower than what's advertised, which can knock your serviceability backwards.
Deposit and LMI with a duplex purchase
You'll generally need at least a 20 per cent deposit to avoid Lenders Mortgage Insurance on an investment loan. For a duplex, that's 20 per cent of the full purchase price, not per dwelling. If you're buying established stock and borrowing above 80 per cent loan to value ratio, expect LMI to add several thousand dollars to your upfront costs, and not all lenders will go that high on an investment duplex anyway.
Consider a buyer looking at a duplex in Shelly Beach within walking distance of the beach. At the area's current median for multi-dwelling properties, a 20 per cent deposit plus stamp duty and settlement costs means you're putting together a six-figure sum before the loan even settles. If you're planning to use equity from your home, the lender will also reassess your owner-occupied property and apply serviceability tests across both loans. That's where the debt-to-income cap can bite: as of February, lenders can only write 20 per cent of new investor loans at six times income or higher, so if your total borrowing pushes you past that threshold, you might get knocked back even if the rental income looks solid on paper.
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Tax treatment under the new rules
The federal tax changes that took effect from 1 July 2027 quarantine rental losses on residential investment properties acquired after 12 May 2026, unless the property is an eligible new build. That means if you buy an established duplex now, you can't offset rental losses against your salary or other income. Losses get carried forward and can only be used against future rental income or capital gains from residential property.
For a duplex, this matters because older stock often runs at a loss in the early years, especially if you're covering body corporate fees, insurance, and interest on a loan above 80 per cent LVR. The quarantining doesn't stop you from claiming deductions like interest, rates, and maintenance, but those deductions can only reduce your rental income to zero. Any excess loss sits in a bucket and waits until you either make a profit or sell the property.
Eligible new builds get different treatment. If the duplex was constructed on previously vacant land, or if it replaced an existing dwelling and increased the total number of dwellings, you can still negatively gear it under the old rules. A knock-down rebuild that replaces one house with one duplex qualifies. A renovation that converts an existing house into two dwellings also qualifies. But a knock-down rebuild that replaces one house with one house does not, even if the new house is bigger.
Fixed versus variable rates for duplex investors
Variable rates give you flexibility to make extra repayments and access offset accounts, which can help if one unit sits vacant for a few weeks or you need to cover an unexpected repair. Fixed rates lock in your repayment amount, but most lenders charge break costs if you pay down the loan early or sell before the fixed term ends.
Shelly Beach has a seasonal rental market because of the holiday crowd, so vacancy rates can tick up outside summer. If you're holding a duplex with one long-term tenant and one short-term tenant, a variable rate with an offset account lets you park rental income and reduce the interest you're paying on the full loan amount. That's more useful than a fixed rate unless you're locking in at a time when rates are clearly about to climb.
Some lenders offer a split rate structure where part of the loan is fixed and part is variable. That can work if you want certainty on the bulk of your repayments but still want access to an offset or the ability to pay down the variable portion without penalty. It's not necessary for everyone, but it's worth looking at if you're managing cash flow across multiple properties.
Interest-only repayments and cash flow
Interest-only repayments keep your monthly outgoings lower because you're not paying down the principal. Most lenders offer interest-only periods of one to five years on investment loans, after which the loan reverts to principal and interest unless you apply to extend it.
For a duplex, interest-only can make sense if you're planning to use the cash flow to fund another purchase or if you're relying on capital growth rather than loan reduction to build wealth. The downside is that your loan balance doesn't drop, so you're not building equity through repayments. You're also paying more interest over the life of the loan compared to principal and interest from day one.
Under the new tax rules, interest remains deductible whether you're on interest-only or principal and interest, so the choice comes down to cash flow and your broader property strategy rather than tax treatment. If you're planning to hold the duplex long-term and you've got other income to cover any shortfall, principal and interest repayments start chipping away at the debt and give you more equity to work with down the track.
What happens if you want to refinance later
Refinancing a duplex works the same way as refinancing any investment property, but the valuation and rental assessment get done fresh. If one unit has been vacant for a while or if the property needs maintenance, the valuer might come in lower than your original purchase price, which can limit how much equity you can access.
Lenders will also reassess your rental income and apply the same serviceability buffer and debt-to-income tests. If rates have gone up since you first borrowed, or if your income has dropped, you might not qualify for the same loan amount even though you've been making repayments without issue. That's something to factor in if you're planning to use the duplex equity to fund another investment in a couple of years.
If you're looking at refinancing to access equity, get the duplex revalued before you lodge an application so you know where you stand. A valuation that comes in under your expectations doesn't stop you from refinancing, but it does mean you'll need to adjust your plans or wait until the market moves.
Structuring the loan if you're buying with someone else
Buying a duplex with a partner, family member, or another investor means the loan needs to reflect who owns what. Most commonly that's a joint loan with both parties listed as borrowers and owners in equal shares, but you can also structure it with unequal shares or with one party guaranteeing the loan without being on the title.
Lenders assess the income and liabilities of everyone on the loan, so if one person has existing debt or a lower income, that affects how much you can borrow. If you're buying with someone who already owns investment property, the lender will factor in their existing loans and rental income as well, which can push you over the debt-to-income cap even if your own position looks fine.
Get advice on the structure before you go hunting for the duplex, because changing it after contracts are exchanged is messy. If you're buying as an investment in a trust or company, you'll need a commercial loan rather than a standard residential investment loan, and the rates and deposits are different.
Call one of our team or book an appointment at a time that works for you. We'll look at your position, run the numbers on a duplex purchase, and talk you through which investment loan options make sense given where the tax rules and serviceability settings sit right now.
Frequently Asked Questions
Can I negatively gear a duplex purchased after May 2026?
Only if it's an eligible new build. Established duplexes bought after 12 May 2026 have rental losses quarantined, meaning you can't offset them against salary or other income. Losses can only be used against future rental income or capital gains from residential property.
Do I need a bigger deposit for a duplex investment loan?
You'll generally need at least 20 per cent of the full purchase price to avoid Lenders Mortgage Insurance. Some lenders will go higher than 80 per cent LVR, but not all will do it on an investment duplex, and you'll pay LMI on the amount above 80 per cent.
How do lenders assess rental income from a duplex?
Lenders assess each dwelling's rental income separately and apply a discount of 20 to 30 per cent to account for vacancy and maintenance. The full loan amount then goes through the serviceability buffer, which adds three percentage points to the product rate.
Should I choose a variable or fixed rate for a duplex loan?
Variable rates give you flexibility for extra repayments and offset accounts, which helps if you have vacancy or unplanned costs. Fixed rates lock in your repayment amount but usually come with break costs if you pay down early or sell before the term ends.
Can I use equity from my home to buy a duplex?
Yes, but the lender will reassess your owner-occupied property and apply serviceability tests across both loans. The debt-to-income cap means lenders can only write 20 per cent of new investor loans at six times income or higher, so your total borrowing matters.
