Duplexes deliver two income streams under one title, but lenders treat them differently depending on whether you buy an existing pair or build from scratch.
The financing structure you choose matters more now than it did twelve months ago. New federal tax rules taking effect from July 2027 will quarantine rental losses on established properties, while preserving full negative gearing for eligible new builds. That distinction changes the way you should approach deposit size, loan structure, and the type of duplex you target.
Why Lenders Value Duplexes Differently
A lender's willingness to fund a duplex depends on whether both dwellings can be separately tenanted and whether the title supports subdivision. If the duplex sits on a single title with two distinct dwellings that can each be rented independently, most lenders will recognise rental income from both. If one side is owner-occupied or the property cannot be separately leased, only the rental portion will be counted toward serviceability.
Consider a buyer purchasing an established duplex on a single torrens title in a growth suburb. Both units are tenanted at the time of purchase. The lender will assess rental income from both dwellings and apply a vacancy factor, typically between 5 and 8 per cent, to calculate net rental income. That income is then added to the borrower's salary for serviceability purposes, after the lender applies a shading factor of around 80 per cent. The loan is assessed as a single investment loan secured against one property, not two separate mortgages.
If the buyer intends to live in one side and rent the other, the lender will treat the arrangement as part owner-occupied and part investment. Only the rental income from the tenanted side will be recognised, and the borrower will need to meet the higher owner-occupied serviceability buffer on the entire loan amount unless the lender agrees to split the facility.
How the July 2027 Tax Changes Affect Duplex Purchases
From 1 July 2027, net rental losses on residential investment properties acquired after 12 May 2026 can only be offset against other residential rental income or carried forward. Losses cannot reduce your salary or other non-residential income for tax purposes. Properties held before that date, including those under contract before 7:30pm AEST on 12 May 2026, continue under the existing negative gearing rules until sold.
The exception is eligible new builds. Duplexes constructed on previously vacant land, or where an existing dwelling has been replaced and the number of dwellings increased, retain full negative gearing. A knock-down rebuild that replaces one dwelling with two qualifies. A knock-down rebuild that replaces two dwellings with two does not.
For a software engineer buying your first investment property, this creates a clear decision point. If you buy an established duplex and both units run at a loss after interest, rates, insurance, and maintenance, you can carry those losses forward to offset future rental profits or capital gains, but you cannot use them to reduce your current taxable salary. If you buy or build a qualifying new duplex, you can offset losses against your salary immediately, reducing your tax each year the property is negatively geared.
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Serviceability Under the DTI Cap
From February 2026, ADIs can fund up to 20 per cent of new investor loans at a debt-to-income ratio of 6 times or greater. If your salary is $180,000, your maximum borrowing under that cap would be $1,080,000 before the lender applies the serviceability buffer. If you also hold owner-occupied debt, that sits in a separate DTI bucket and does not count toward the investor 20 per cent allocation.
In our experience, software engineers with RSU income or substantial bonuses often sit just above the DTI threshold when buying a duplex. The duplex purchase price sits above the median for a single dwelling, and rental income is shaded for serviceability even though both units are tenanted. Lenders that recognise unvested RSUs or bonuses in their income assessment can bring borrowing capacity back under the cap, but not all lenders will do so. Understanding your income structure before you apply improves the chance your application falls within the lender's allocation.
In a scenario like this, a borrower earning a base salary of $160,000 with $40,000 in annual RSUs applies for a loan of $950,000 to purchase a duplex. If the lender includes the full $200,000 in income, the DTI sits at 4.75 times and the loan falls within the standard allocation. If the lender only recognises the base salary, the DTI rises to 5.94 times, which still sits below the 6 times cap but reduces the borrower's access to rate discounts and may require manual approval.
Structuring the Loan for Maximum Flexibility
Most duplex investors choose interest-only repayments for the first five years to maximise their deductible interest and preserve cash flow. Because interest on investment borrowings is fully deductible, paying down principal offers no tax advantage during the period the property is negatively geared. Switching to principal and interest repayments makes sense once the property becomes cash-flow positive or when you plan to convert it to your primary residence.
Some lenders allow you to split the facility so that each dwelling is effectively funded by a separate loan tranche. This is useful if you intend to sell one side later, refinance one dwelling, or convert one side to owner-occupied. The split must be established at the time of settlement. Retrospectively splitting a loan is rarely permitted.
A split structure also allows you to fix the rate on one tranche and keep the other variable. If one unit has a stable long-term tenant and the other has higher turnover, you can lock in repayments on the stable side and retain flexibility on the other. Fixed rates currently sit below variable rates for terms of two to three years with most major lenders, but fixing removes your ability to make additional repayments without incurring break costs.
Deposit and LMI Considerations
Most lenders cap investor lending at 90 per cent LVR, meaning you need at least a 10 per cent deposit plus costs. If you are using RSUs and bonuses as genuine savings, those funds must typically be held in your account for at least three months before settlement unless the lender accepts a signed vesting schedule as evidence of incoming funds.
Lenders Mortgage Insurance is charged on a higher scale for investment loans than for owner-occupied loans. At 90 per cent LVR, LMI on an investment loan can add 3 to 4 per cent of the loan amount to your upfront costs. Some lenders offer LMI waivers for tech industry workers in specific professions, but those waivers typically apply to owner-occupied lending only. If you hold equity in an existing property, releasing that equity to fund the deposit avoids LMI on the new purchase, though the equity loan itself will be subject to LMI if the combined LVR exceeds 80 per cent.
Settlement costs for a duplex include stamp duty calculated on the full purchase price, conveyancing, building and pest inspection for both dwellings, and lender fees. If the duplex is in New South Wales or Victoria, foreign purchaser duty does not apply to citizens or permanent residents, but the property may be subject to land tax once annual land value exceeds the threshold.
Rental Income Recognition and Vacancy Rates
Lenders apply a vacancy factor to rental income to account for periods when the property is untenanted. The standard vacancy rate is between 5 and 8 per cent, but it can rise to 10 per cent for properties in regional areas or where tenancy history is limited. The lender will request a rental appraisal or rely on the lease agreements in place at settlement.
For a duplex generating $1,200 per week in combined rent, a lender applying a 7 per cent vacancy factor and an 80 per cent shading factor will recognise $46,272 in annual rental income for serviceability purposes. That figure is added to your salary and other income, then assessed against your existing liabilities and the serviceability buffer.
If one side of the duplex is vacant at the time of application, some lenders will exclude that unit's rental income entirely until a lease is signed. Others will accept a rental appraisal from a licensed property manager. The approach varies by lender, so having both units tenanted at the time of application improves your borrowing capacity.
Should You Build or Buy Established?
The decision between buying an established duplex and building a new one depends on your timeline, risk tolerance, and how you intend to use the negative gearing provisions.
Building a duplex on vacant land or through a knock-down rebuild that increases dwelling numbers preserves full negative gearing under the new rules. Construction loans are drawn down progressively as the build reaches each stage, so you only pay interest on the amount drawn. Most lenders allow interest-only repayments during construction, and the loan converts to principal and interest or remains interest-only once the build is complete. Construction loans for tech industry workers typically require a higher deposit, often 20 per cent, and the lender will require fixed-price contracts, council approval, and builder's warranty insurance before approving the loan.
Building takes longer and introduces completion risk, but the tax treatment from July 2027 makes it worth considering if your salary is high enough to benefit from negative gearing. Buying an established duplex is faster and removes construction risk, but if you purchase after 12 May 2026, you will not be able to offset losses against your salary once the new rules commence.
Call one of our team or book an appointment at a time that works for you. We'll walk through your income structure, the duplex options you're considering, and how the lending and tax settings align with what you're building.
Frequently Asked Questions
Can I negatively gear a duplex purchased after May 2026?
You can carry rental losses forward to offset future rental income or capital gains, but you cannot offset them against your salary unless the duplex is an eligible new build. Duplexes held before 12 May 2026 continue under the existing negative gearing rules.
How do lenders assess rental income from both units?
Lenders recognise rental income from both dwellings if they can be separately tenanted. They apply a vacancy factor of 5 to 8 per cent and a shading factor of around 80 per cent, then add the net figure to your salary for serviceability.
What deposit do I need for a duplex investment loan?
Most lenders cap investor lending at 90 per cent LVR, so you need at least a 10 per cent deposit plus settlement costs. If you borrow above 80 per cent LVR, you will pay Lenders Mortgage Insurance on the investor scale.
Should I fix or keep the loan variable?
Interest-only variable loans offer the most flexibility for investors. Some lenders allow you to split the facility so you can fix one tranche and keep the other variable, which suits duplexes where one unit has stable tenancy and the other has higher turnover.
Does the DTI cap apply to duplex purchases?
Yes. From February 2026, lenders can fund up to 20 per cent of new investor loans at a debt-to-income ratio of 6 times or greater. Duplex purchases often sit above the median, so your income structure and how the lender recognises RSUs or bonuses will affect whether you fall within the cap.
