Common Mistakes When Buying a Duplex for Investment

A duplex can deliver two income streams from one title, but the loan structure you choose determines whether that advantage translates into cashflow or just additional complexity.

Carnegie's stock of weatherboard and brick duplexes, particularly around Koornang Road and the streets running toward Caulfield, has attracted investors for years. The suburb's proximity to Monash University, established transport links, and relatively affordable entry point compared to neighbouring Glen Huntly or Caulfield North make it a practical choice for those looking to build rental income without stretching into premium suburbs. A duplex in this area typically offers the option to rent both units separately or hold one for future owner-occupation while the other generates income.

The 2026-27 Federal Budget introduced changes to negative gearing and capital gains tax that apply to established residential properties purchased after 12 May 2026. If you're considering a duplex purchase now, those changes will affect how losses are claimed and how gains are taxed from 1 July 2027. New builds remain eligible for the existing 50% CGT discount and full negative gearing arrangements, which makes the distinction between an established duplex and a newly constructed one more relevant than it has been in recent years.

Should You Split the Duplex into Separate Loans?

If both units sit on one title, most lenders will treat the duplex as a single security. You can choose to take out one loan for the full amount or split the borrowing into two separate facilities secured against the same property. The second option gives you flexibility if you later decide to sell one unit after subdivision or refinance one loan without touching the other.

Consider a scenario where you purchase a duplex for close to the current median in Carnegie. You place a 20% deposit to avoid Lenders Mortgage Insurance and borrow the remainder. If you structure this as two loans of equal value, each loan sits at a lower loan to value ratio, which can make refinancing or equity release more straightforward down the line. It also means you can assign one loan to interest-only and the other to principal and interest, depending on your cashflow and tax position.

Separate loans do not change your overall borrowing capacity, but they do allow you to treat each income stream independently when it comes to repayment strategy. If one unit becomes vacant, you can prioritise paying down that loan while keeping the other on interest-only to preserve cashflow.

How the Recent Budget Changes Affect Duplex Purchases

From 1 July 2027, losses from established residential properties purchased after Budget night can only be offset against rental income or capital gains from residential property, not against wage income. If you buy an established duplex in Carnegie now, any net rental loss from that property will need to be carried forward or offset against other residential property income from that date.

The change does not apply to new builds. If you're purchasing a newly constructed duplex or planning to build a dual-occupancy development on a vacant block, you retain access to full negative gearing and the existing 50% CGT discount when the property is eventually sold. This creates a material difference in after-tax returns depending on whether the duplex you're considering is established or new.

For properties purchased before 12 May 2026, existing arrangements remain in place. The new rules apply only to contracts entered into from 13 May 2026 onward, and even then, the impact does not take effect until mid-2027. If you're in the process of securing finance for a duplex now, it's worth confirming the contract date and speaking with a tax adviser to understand how the transition will affect your deductions.

Interest-Only or Principal and Interest for Dual Income Properties

Interest-only loans reduce your monthly outgoings, which can be useful if rental income does not cover the full loan repayment and you want to preserve cashflow in the early years. Many investors choose interest-only for investment properties to maximise the interest component of their tax deductions, then switch to principal and interest later when income increases or they want to reduce debt.

With a duplex generating two separate rental incomes, the case for interest-only becomes more nuanced. If both units are tenanted and the combined rent covers the interest and holding costs, you may prefer to pay down principal to build equity faster. If one unit sits vacant or you plan to occupy one side while renting the other, interest-only on the investment portion gives you flexibility to manage the non-income-producing holding cost.

You can also split the loan structure. In a scenario where you borrow using two separate facilities, one could remain interest-only while the other moves to principal and interest. This allows you to reduce debt on one side while keeping repayments lower on the other, depending on which unit generates stronger rental demand or which you intend to sell first.

Interest-only periods typically last between one and five years, depending on the lender. After that period, the loan reverts to principal and interest unless you apply to extend. Not all lenders will approve an extension, particularly if your income or the property's rental yield has changed since the original application. Planning for that reversion point is part of structuring the loan properly from the outset.

What Lenders Look for When Assessing Duplex Investment Loans

Lenders assess duplex purchases using the same serviceability criteria as any other investment loan, but they treat rental income differently depending on whether both units are tenanted at the time of application. Most lenders will apply a shading factor to rental income, usually between 70% and 80%, to account for vacancy and maintenance costs. If only one unit is leased, they may use market rent for the second unit but apply a higher discount.

Your borrowing capacity depends on your income, existing debts, and the rental yield of the duplex. If the property is in an area with a higher vacancy rate, some lenders may reduce the income assumption further. Carnegie's rental market is generally stable due to its proximity to Monash University and public transport, but lenders will still factor in the possibility of one or both units sitting empty for part of the year.

If you already own property and are using equity to fund the deposit, the lender will assess your overall portfolio, not just the new purchase. Cross-collateralisation can occur if you use an existing property as additional security, which may limit your ability to sell or refinance later without the lender's consent. Keeping securities separate where possible gives you more control over your portfolio as it grows.

Common Loan Features Worth Considering for Duplex Finance

An offset account linked to your investment loan allows you to park surplus cash and reduce the interest charged without making additional repayments. If you're holding funds for future property purchases or managing irregular income, an offset can reduce your interest cost while keeping cash accessible. Not all investment loan products offer offset accounts, and those that do may charge a higher interest rate or annual fee.

A redraw facility lets you access extra repayments you've made above the minimum, but it does not reduce the interest charged in the same way an offset does. Redraw can be useful if you plan to pay down the loan faster and want the option to pull funds back out for renovations or further investment, but it lacks the flexibility of an offset and may have restrictions on how much you can withdraw.

If you're planning to subdivide the duplex in future, portability becomes relevant. Some lenders allow you to transfer a loan to a different security without reapplying, which can make the process of splitting the title and assigning each loan to a separate unit more straightforward. Confirming portability and split loan options at the application stage saves time later.

Managing Holding Costs and Tax Deductions on a Duplex

Most expenses related to an investment property are claimable, including loan interest, body corporate fees if applicable, council rates, insurance, and maintenance. Depreciation on the building and fixtures can also be claimed if you obtain a quantity surveyor's report, though changes to depreciation rules in recent years have limited claims on second-hand assets.

With a duplex, you may have separate utility meters and body corporate arrangements depending on how the property is structured. If the duplex is on a single title with shared services, you'll need to apportion costs between the two units when claiming deductions. If the title has been subdivided and each unit has its own services, tracking costs becomes more straightforward.

Stamp duty is payable on the full purchase price at the time of settlement and is not deductible in the year of purchase. It can be added to the cost base of the property for capital gains tax purposes, which reduces the taxable gain when you eventually sell. In Victoria, stamp duty on investment properties is calculated at the standard residential rate unless the property is newly built and eligible for concessions.

Refinancing a Duplex Investment Loan

Refinancing can make sense if your current loan no longer suits your strategy or if you can access better investor interest rates elsewhere. Lenders regularly adjust their pricing, and the rate you were offered at purchase may not reflect what's available now. Refinancing also allows you to access equity if the duplex has increased in value or if you've paid down the loan.

If you initially set up the duplex on one loan and now want to split it into two, refinancing is the point at which that restructure happens. You can move both loans to a new lender or keep one with the existing lender and move the other. The latter option can be more involved, as it requires the original lender to release part of the security.

Refinancing costs include application fees, valuation fees, and discharge fees from your existing lender. Some lenders offer cashback incentives or waive application fees to attract refinance customers, but those offers should be weighed against the ongoing rate and loan features rather than treated as the primary reason to switch.

Call one of our team or book an appointment at a time that works for you to discuss how the loan structure, repayment type, and recent tax changes apply to your situation and the duplex you're considering in Carnegie.

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