When you apply for an investment loan, lenders run a different set of calculations than they do for an owner-occupier purchase. Rental income is only partially counted, existing debt across your portfolio weighs heavily, and serviceability buffers apply to every loan you hold. The gap between what investors expect to borrow and what lenders will approve can be significant, and understanding why makes it easier to plan your next purchase realistically.
How Rental Income Is Assessed
Most lenders do not count 100% of a property’s rental income when calculating your ability to service an investment loan. The standard approach is to shade rental income by 20% to 30%, meaning a property earning $600 per week would be assessed on $420 to $480 per week. This discount accounts for vacancy periods, property management fees, maintenance costs, and the risk of income interruption.
Some lenders use a Net Rental Income calculation that factors in actual loan repayments and deductible costs. Others apply the Household Expenditure Measure (HEM) framework, where rental income is treated as gross income subject to a notional tax rate. The method varies by lender and affects the final borrowing capacity figure, sometimes by a meaningful amount. Up-to-date property management statements and a current rental appraisal letter give lenders the most accurate picture and help avoid conservative assumptions being applied.
The Serviceability Buffer Applies to Your Whole Portfolio
Since late 2021, APRA has required lenders to assess a borrower’s ability to service a new loan at 3 percentage points above the actual interest rate, or a floor rate of 5.5%, whichever is higher. This buffer applies to the new loan being assessed and has a compounding effect for investors with existing debt.
If you have a home loan at 6.1% and are applying for an investment loan at 6.3%, the lender assesses your capacity to service both loans at 9.1% and 9.3% respectively. Each loan in your portfolio increases the assessed debt obligation. For investors with 2 or 3 properties, the accumulated impact of the buffer across the whole portfolio can substantially reduce what is available for the next purchase, even when the actual cash flow from those properties is positive.
Buffer impact on a 2-property investor
Existing home loan: $600,000 at 6.1%, assessed at 9.1% = $5,490/month assessed repayment.
Existing investment loan: $500,000 at 6.3%, assessed at 9.3% = $4,650/month assessed repayment.
Combined assessed debt servicing before any new borrowing: $10,140/month. The buffer turns manageable real-world repayments into a demanding assessment hurdle.
Debt-to-Income Ratios and Where Lenders Draw the Line
APRA has flagged debt-to-income (DTI) ratios as a key risk indicator in investment lending, and many lenders now apply internal caps on total debt relative to gross income. The typical range is 6 to 8 times annual income, though the specific cap varies by lender and can also vary based on the borrower’s credit profile and loan structure.
A borrower earning $150,000 per year with $900,000 in existing debt is sitting at a DTI of 6, at or near the ceiling for some lenders before any new borrowing. For that borrower, being declined at one lender does not mean being declined everywhere. DTI caps differ, and some lenders assess the ratio differently when rental income is taken into account. This is one area where comparing lenders through a broker can make a direct difference to what is achievable.
How Interest-Only Loans Affect Assessed Capacity
Investors frequently use interest-only (IO) loan terms to manage cash flow and tax outcomes. But lenders typically do not assess borrowing capacity based on the IO repayment. Instead, they assess on a principal-and-interest (P&I) basis over the remaining loan term after the IO period expires.
A $600,000 investment loan on a 30-year term with a 5-year IO period would be assessed as a 25-year P&I loan once the IO period ends. The assessed monthly repayment for that remaining period is higher than the interest-only repayment during the IO phase. Lenders apply this higher figure when calculating whether you can service the debt, which reduces assessed borrowing capacity relative to what the actual IO repayments would suggest. It is worth understanding this distinction before modelling what your next purchase might look like.
Strategies Investors Use to Improve Their Position
There are practical steps that can improve a borrowing capacity assessment before applying. Reducing high-interest unsecured debt removes assessed liabilities from the calculation and can shift the DTI ratio meaningfully. Providing accurate rental income evidence through current management statements and rental appraisal letters ensures lenders are working from real figures rather than conservative estimates.
Loan structure also plays a role. Keeping investment debt clearly separated from owner-occupier debt assists both the assessment process and the tax treatment of interest deductions. Some investors spread lending across more than one lender to manage DTI exposure at individual institutions. This approach requires careful structuring and is worth working through with both a mortgage broker and a qualified accountant before acting on it.
| Assessment Factor | How Investors Are Treated |
|---|---|
| Rental income | Shaded by 20-30%; only 70-80% counted |
| Serviceability buffer | 3% above rate or 5.5% floor, applied to all existing loans |
| DTI cap | Typically 6-8x gross annual income across all debt |
| IO loan assessment | Assessed at P&I repayments on remaining term after IO period |
| Negative gearing | Tax benefit does not directly increase assessed borrowing capacity |
Key Takeaways
- Rental income is shaded by 20-30% by most lenders. A property earning $600 per week may only be counted at $420-$480 per week in a borrowing capacity assessment.
- The 3% serviceability buffer applies to all existing and new debt. A multi-property portfolio significantly increases assessed obligations even when real cash flow is positive.
- Many lenders cap total debt at 6 to 8 times gross annual income. Investors approaching those limits may find their options vary significantly by lender.
- Interest-only loans are typically assessed on a P&I basis over the remaining loan term after the IO period, which can reduce assessed borrowing capacity relative to actual IO repayments.
- Reducing unsecured debt and providing accurate rental income documentation are practical steps that can improve the outcome before applying.
- Investors should work with both a mortgage broker and a qualified accountant when structuring new investment lending, particularly where deductibility and loan separation are relevant.