Interest-only home loans can reduce your monthly repayments, sometimes by hundreds of dollars. But there is a catch that many borrowers do not discover until they apply for finance.
Lower repayments do not necessarily mean you can borrow more.
In fact, an interest-only loan can sometimes make it harder to satisfy a lender's borrowing capacity assessment than an equivalent principal and interest loan.
That sounds strange.
If you are paying less every month, shouldn't the bank consider the loan more affordable?
The answer comes down to the difference between what you actually repay and what the lender uses to assess your ability to repay the debt.
For property investors, this distinction can be particularly important. A purchase that appears affordable using interest-only repayments may not satisfy the lender's serviceability requirements.
Before deciding on a repayment structure, it helps to understand what the lender is actually calculating.
An interest-only loan may improve your short-term cash flow. It does not automatically improve borrowing capacity, because lenders generally assess your ability to repay the principal as well.
How Does an Interest-Only Home Loan Work?
With a standard principal and interest home loan, each scheduled repayment contains two components:
- Interest: the cost of borrowing the money.
- Principal: the amount that reduces your outstanding loan balance.
With an interest-only loan, scheduled repayments during the interest-only period generally cover the interest charged on the loan.
You are not required to make scheduled principal repayments during that period, although voluntary repayments may be possible depending on the loan terms.
Interest-only periods are commonly offered for a limited number of years, often between one and five years, depending on the lender and product.
When the interest-only period finishes, the loan normally converts to principal and interest repayments over the remaining loan term.
What happens to the loan balance?
Suppose you borrow $650,000 and make only the required interest payments for five years.
Assuming no additional repayments, capitalised amounts or other changes, you will still owe $650,000 at the end of those five years.
The interest has been paid, but the principal has not reduced.
That is the fundamental difference between interest-only and principal and interest lending.
Principal and Interest
Your repayments cover interest and gradually reduce the loan balance. You build equity through principal repayments, assuming no redraws or further borrowing.
Interest Only
Your required repayments are generally lower during the interest-only period, but the principal does not reduce through scheduled repayments.
Why Interest Only Usually Does Not Increase Borrowing Capacity
This is where the misunderstanding begins. Borrowers often calculate how much they can afford using the repayment they expect to make. Lenders generally use a different calculation.
They need to assess whether the borrower can meet the loan repayments over the relevant term, including when the interest-only period ends.
For many Australian lenders, this means assessing an interest-only loan using principal and interest repayments over the remaining term.
The remaining loan term matters
Consider a 30-year loan with five years of interest-only repayments. After five years, the borrower still owes the original principal, assuming no voluntary reductions.
But only 25 years remain to repay it.
The lender may therefore calculate serviceability using the repayment required to repay the full principal over those remaining 25 years, rather than the initial interest-only repayment.
This can result in a higher assessed repayment than for an equivalent 30-year principal and interest loan.
A lower actual repayment can sit alongside a higher assessed repayment. That is why switching to interest only is not a reliable way to increase your borrowing capacity.
Lender policies are not identical. Some lenders apply different serviceability calculations, product rules or assessment requirements.
The actual outcome depends on the lender, the loan structure and the borrower's overall circumstances.
Worked Example: $650,000 Interest Only vs Principal and Interest
Let's compare two borrowers who each take out a $650,000 home loan.
Both loans have an original 30-year term and an illustrative interest rate of 6.50% per annum.
One borrower chooses principal and interest repayments from the beginning.
The other chooses five years of interest-only repayments, followed by principal and interest repayments over the remaining 25 years.
Example Loan Details
| Loan Detail | Assumption |
|---|---|
| Loan amount | $650,000 |
| Original loan term | 30 years |
| Illustrative interest rate | 6.50% p.a. |
| Interest-only period | 5 years |
| Remaining term after interest only | 25 years |
Monthly Repayment Comparison
| Repayment Type | Monthly Repayment |
|---|---|
| Principal and interest over 30 years | $4,108 |
| Interest only during first five years | $3,521 |
| Principal and interest over remaining 25 years | $4,389 |
During the first five years, the interest-only borrower pays approximately $588 less per month.
That can make a meaningful difference to cash flow.
But once the interest-only period finishes, repayments increase from approximately $3,521 to $4,389 per month.
That is an increase of about $868 per month, or approximately 25%, assuming the interest rate remains unchanged.
The new repayment is also approximately $280 per month higher than the original 30-year principal and interest repayment.
The reason is straightforward: the borrower now has fewer years to repay the same principal amount.
Calculations are illustrative and rounded. They assume monthly repayments, a constant 6.50% interest rate, no fees, no offsets, no voluntary principal reductions and no change in loan terms. Actual lender repayments and assessment methods differ.
The Interest Rate Used for Borrowing Capacity Is Different
There is another important part of the serviceability calculation.
Australian lenders generally do not assess a home loan solely at its advertised interest rate.
They typically apply a serviceability buffer to account for the possibility that interest rates may increase.
APRA's prudential framework has required authorised deposit-taking institutions to use an interest rate buffer of at least three percentage points above the loan rate, subject to applicable regulatory requirements.
Lenders may also apply assessment floors or additional requirements.
Non-bank lenders can use different assessment methods, depending on their funding arrangements and credit policies.
An illustrative assessment
Suppose the actual loan rate is 6.50%.
Adding a three percentage point buffer produces an illustrative assessment rate of 9.50%.
The lender may then assess the loan using principal and interest repayments over the relevant term.
For an interest-only loan, that term may be the remaining principal repayment period after interest only ends.
The resulting assessed repayment can be considerably higher than the amount the borrower actually pays today.
The assessment rate is not necessarily the interest rate you will pay. It is a lending calculation used to test repayment capacity.
The applicable regulatory buffer and each lender's current policy should be verified at the time of application.
When Can Interest-Only Repayments Be Useful?
Interest-only lending is not inherently unsuitable.
It can serve legitimate purposes, particularly where a borrower has a clearly understood cash-flow requirement.
The important distinction is between using interest only to manage repayments and expecting it to increase borrowing capacity.
1. Managing investment property cash flow
Investment properties have ongoing costs beyond the loan repayment.
These may include council rates, insurance, property management fees, repairs and periods without a tenant.
An interest-only loan may reduce scheduled loan repayments during the interest-only period.
That can leave more cash available to manage other property expenses.
However, the investor still needs to consider the eventual increase in repayments and the long-term interest cost.
2. A temporary reduction in household income
Some borrowers experience periods when their income is expected to change.
Examples may include parental leave, a temporary reduction in working hours or a career transition.
Interest-only repayments may provide short-term cash-flow flexibility, subject to lender approval.
But the borrower must still satisfy the lender's repayment assessment, including the expected principal and interest commitments.
If you are planning a property purchase around maternity or parental leave, read our guide to getting a home loan while on parental leave .
3. Construction finance
Interest-only repayments are common during residential construction.
This is because the loan is often drawn progressively as building stages are completed.
The borrower may initially pay interest only on the funds that have been drawn.
Once construction is completed, the loan generally moves to its agreed ongoing repayment structure.
Our guide to construction loans and progress payments explains how staged funding works.
Construction interest-only arrangements should not be confused with assuming a lender will approve a larger loan simply because repayments are lower during the build.
Interest-Only Loans for Investment Properties
Interest-only lending is frequently discussed in the context of property investing.
For some investors, the main attraction is the ability to reduce scheduled repayments during the initial holding period.
But there are several factors to consider.
- Investment interest rates may differ from owner-occupier rates.
- Interest-only products may have different pricing and loan-to-value ratio requirements.
- The loan balance generally does not reduce through scheduled repayments during the interest-only period.
- The lender may assess the loan using principal and interest repayments over a shorter remaining term.
- The property may affect borrowing capacity for future purchases.
What if the investment property is negatively geared?
A negatively geared property generally has deductible expenses exceeding its rental income.
Interest-only repayments can affect cash flow, but they do not make a loss-making property profitable.
The tax treatment of investment losses is a separate question.
For an explanation of the mechanism and the 2026 tax reforms, read how negative gearing works in Australia .
The suitability of an investment strategy and the tax implications should be reviewed with appropriately qualified professionals.
Are Interest-Only Loans More Tax Effective?
This is a common question among property investors.
The general principle under Australian tax law is that interest on borrowings used for an income-producing purpose may be deductible, subject to the relevant rules.
Principal repayments are generally not tax deductions.
However, that does not automatically make interest-only lending the better choice for an investor.
The tax treatment depends on the purpose of the borrowing, how the funds are used and the investor's circumstances.
For example, some investors may seek to manage deductible investment debt differently from private home debt.
That can raise complex questions about interest deductibility, offset accounts, redraw facilities and loan purpose.
Triple O Finance does not recommend interest-only lending as a tax strategy or advise whether a particular loan structure will produce a tax benefit.
A registered tax agent should review the tax implications of any proposed loan structure before you proceed.
Why Construction Loans Often Start as Interest Only
Construction loans operate differently from ordinary established-property loans.
Rather than advancing the entire construction amount at settlement, the lender typically releases funds in stages.
These stages may include slab, frame, lock-up, fit-out and completion, depending on the building contract.
During construction, interest may be charged on the amount drawn, rather than the entire approved construction limit.
For example, if a borrower has drawn $200,000 of a $500,000 construction facility, interest may be calculated on the drawn balance, subject to the loan terms.
This arrangement can reduce the repayment burden while the property is being built.
However, lenders generally assess the borrower's capacity to manage the completed loan commitments.
The temporary construction repayment is therefore not a reliable indication of the borrowing capacity available for the finished home.
The Hidden Costs of Interest-Only Home Loans
The lower repayment during an interest-only period can be attractive.
But focusing only on the first few years can hide the longer-term financial consequences.
1. Your principal does not reduce
With principal and interest repayments, part of each payment reduces the loan balance.
With interest-only repayments, the balance generally stays the same unless additional principal payments are made.
That means you are not building equity through scheduled principal repayments during the interest-only period.
Your equity may still change as property values move, but property growth is not guaranteed.
2. Your repayments increase when interest only ends
At the end of the interest-only period, the remaining principal generally needs to be repaid over fewer years.
This can create a significant repayment increase.
If interest rates have also risen, the increase may be greater.
Borrowers should understand the expected post-interest-only repayment before entering the loan.
3. You may pay more interest over the loan term
Because the balance does not reduce during the interest-only period, interest continues to be calculated on a higher outstanding amount.
Over the same overall loan term, this can produce a materially higher total interest cost.
30-Year Total Interest Comparison
Using the same $650,000 loan at a constant 6.50% interest rate:
| Loan Structure | Approximate Total Interest |
|---|---|
| Principal and interest for 30 years | $829,039 |
| 5 years interest only, then 25 years P&I | $877,904 |
| Additional interest with interest only | $48,865 |
In this example, the borrower pays approximately $48,865 more interest over the original 30-year term by choosing five years of interest-only repayments.
The actual difference could be higher or lower depending on interest rates, loan pricing, repayment changes, offset balances and other factors.
Illustrative amortisation comparison only. Both loans are assumed to have the same 6.50% interest rate throughout, with no fees, offsets, extra repayments or term extensions. Interest-only loans may have different actual rates. Figures are rounded.
4. Interest-only pricing may be higher
Some lenders charge higher interest rates for interest-only loans compared with principal and interest products.
This can increase the overall cost further.
Borrowers should compare the actual loan products, not just repayment types using an identical rate.
5. Refinancing may become harder
A borrower who plans to refinance at the end of the interest-only period needs to consider future lender requirements.
Their income, property value, existing debts and credit history may have changed.
Lender policies and interest rates may also be different.
If refinancing is part of the plan, understand the risks rather than assuming another lender will approve the application.
Our home loan refinancing guide explains the general process and considerations.
Can You Extend an Interest-Only Period?
Potentially, but an extension is not automatic.
Some lenders may allow borrowers to apply for another interest-only period, subject to their policy.
The lender may reassess the borrower's financial circumstances, repayment capacity and loan details.
A borrower who qualified for interest only five years earlier may not necessarily qualify for an extension.
The loan-to-value ratio, income, expenses and remaining loan term may all be relevant.
It is therefore important to prepare for the scheduled principal and interest repayments rather than relying on an extension.
What Actually Improves Home Loan Borrowing Capacity?
If the main problem is borrowing capacity, switching to interest only may not solve it.
There are other factors that can have a more meaningful impact on the lender's assessment.
1. Reviewing credit card limits
Lenders generally assess credit card commitments using the approved credit limit, not just the outstanding balance.
For example, a borrower with a $20,000 credit card limit may have that limit included in servicing even if the balance is currently zero.
Reducing or closing unused limits may improve borrowing capacity in some circumstances.
However, the effect depends on lender policy and the borrower's overall position.
2. Reviewing personal loans and vehicle finance
Car loans, personal loans and other repayment commitments can reduce the income available for a proposed mortgage.
A loan nearing its final repayment may be assessed differently from one with several years remaining, depending on the lender.
Repaying or restructuring existing debt may improve serviceability, but fees, interest costs and the use of savings should also be considered.
3. Choosing a lender that understands your income
This can be particularly important for borrowers whose income is not a simple fixed salary.
Different lenders can assess overtime, shift allowances, bonuses and other variable income differently.
One lender may accept a greater portion of an established income component than another, subject to evidence and policy requirements.
The difference can materially affect borrowing capacity.
4. Reviewing existing investment loans
If you already own investment properties, the way lenders assess their rental income and loan commitments can affect your next purchase.
Some lenders apply different rental income adjustments and servicing methods.
Comparing these policies can be more useful than simply changing the repayment type on the proposed loan.
5. Checking the overall loan structure
Loan term, existing liabilities, deposit size, interest rate and lender assessment policy can all influence the result.
There is no single change that guarantees a higher borrowing figure.
The appropriate approach is to assess the full financial position against relevant lender requirements.
Why Lender Selection Matters for Police, Nurses and Other Professionals
At Triple O Finance, we regularly work with borrowers whose income includes more than their base salary.
This includes police officers, nurses, paramedics, firefighters, doctors and other professionals.
Their income may include:
- Regular overtime.
- Shift penalties.
- Weekend and public holiday allowances.
- Higher duties allowances.
- Other eligible employment allowances.
These income components can be treated differently between lenders.
For example, a borrower may have a base salary of $95,000 and receive an additional $25,000 in regular overtime and allowances.
The lender's assessment may depend on the type of income, its history, consistency and supporting documentation.
One lender may accept more of the variable income than another.
That difference may be more important to borrowing capacity than whether the proposed loan is interest only or principal and interest.
If your borrowing capacity appears lower than expected, it is worth checking how the lender has assessed your actual income.
For borrowers receiving regular overtime or shift penalties, lender selection can make a material difference. Acceptance is always subject to the specific lender's policy.
Interest Only vs Principal and Interest: Which Is Better?
Neither repayment type is automatically better for every borrower.
The choice depends on the loan purpose, repayment objectives, cash-flow requirements and lender eligibility.
| Consideration | Interest Only | Principal and Interest |
|---|---|---|
| Initial required repayments | Generally lower | Generally higher |
| Scheduled principal reduction | No, during IO period | Yes |
| Repayments after IO period | Generally increase | Amortised throughout the term |
| Total interest over same loan term | Generally higher, all else equal | Generally lower, all else equal |
| Short-term cash flow | Lower scheduled outgoings | Higher scheduled outgoings |
| Borrowing capacity | Not automatically higher | Depends on lender assessment |
| Equity built through repayments | None during IO period unless extra payments are made | Builds as principal is repaid |
| Tax considerations | Require accountant advice | Require accountant advice |
For some borrowers, the lower scheduled repayment during an interest-only period may provide useful flexibility.
For others, the additional interest cost and repayment increase may outweigh that benefit.
The important point is to understand both the immediate and long-term commitments.
Questions to Ask Before Choosing an Interest-Only Loan
Before selecting an interest-only repayment structure, consider these questions.
- Why do I want interest only? Is the goal short-term cash flow, construction funding or something else?
- What will my repayments be when the interest-only period ends? Calculate the future principal and interest repayment before committing.
- Can I afford the higher repayment? Consider what happens if interest rates rise or household income changes.
- How much additional interest could I pay? Compare the total cost over the same loan term.
- Will the lender assess the loan differently? Understand the actual serviceability calculation rather than assuming lower repayments increase capacity.
- Am I relying on refinancing later? Consider what happens if future lending requirements cannot be met.
- Have I obtained independent tax advice? If tax treatment is part of the reasoning, have a registered tax agent review it.
These questions help establish whether the repayment structure is consistent with your borrowing circumstances.
They do not replace individual credit assessment or professional tax and financial advice.
How Triple O Finance Can Help
Interest-only loans are not simply about paying less today.
They involve trade-offs between cash flow, future repayments, total interest cost and lender assessment.
At Triple O Finance, we can help you understand how different lenders assess your income, existing debts and proposed loan structure.
Our credit assistance may include:
- Comparing relevant principal and interest and interest-only home loan options.
- Explaining lender serviceability requirements.
- Assessing borrowing capacity using relevant lender policies.
- Reviewing how overtime, shift allowances and variable income are treated.
- Explaining repayment changes at the end of an interest-only period.
- Reviewing refinancing options for existing home and investment loans.
Where tax or investment strategy questions arise, we recommend obtaining advice from the appropriate qualified professional.
Not Sure Whether Interest Only Is Right for Your Loan?
The first step is understanding how lenders will assess your actual financial position, not just comparing monthly repayments.
We can help you compare relevant lender policies and understand the borrowing options available for your circumstances.
Get a Free Assessment
Written by Nishant Ramavat
Founder, Director & Senior Finance Specialist
Triple O Finance
Nishant is the Founder, Director and Senior Finance Specialist at Triple O Finance. A former NSW Police Officer, he has worked in mortgage broking since establishing the business in 2018.
He helps Australian borrowers, including emergency services professionals and property investors, understand lender policies, borrowing capacity and home loan options.
