The quick answer
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Extra repayments can reduce the interest on a home loan, subject to the product’s rules. Investing offers uncertain returns and can involve tax, fees and losses. Comparing a mortgage rate with a headline investment return therefore misses important differences. Start with required repayments, essential costs and accessible cash. Then compare the same money over the same period, using clearly stated tax and cost assumptions. This is a decision framework, not a recommendation to choose one path.
First separate required repayments from extra money
The decision only concerns money left after meeting actual commitments. A household that has $1,000 left before an annual insurance bill has not necessarily got $1,000 available to invest. Include irregular expenses and minimum debt repayments in the starting budget.
Also distinguish an extra principal repayment from cash in an offset. Both may reduce interest, but they differ in access and contractual treatment. If the money is your only emergency reserve, moving it into a loan can change how readily it is available. Read the agreement rather than assuming redraw is an unrestricted savings account.
A useful first sentence is: “After required costs and the reserve we want to retain, we can allocate this amount for this many years.” It gives both paths the same starting point and prevents an optimistic saving assumption from deciding the result.
What does reducing a home loan actually save?
For a simplified owner-occupied loan with no interest deduction, reducing the interest-bearing balance by $10,000 at an unchanged 6% rate avoids about $600 of interest over a full year. The exact amount depends on repayment timing, daily balances and the lender calculation.
This is not the same as receiving $600 cash into your account. The benefit may appear as more of the scheduled repayment reducing principal. Your lender might also recalculate required repayments under its own arrangements. Ask how the extra payment affects both the repayment and remaining term.
MoneySmart notes that extra repayments can save interest and help a loan finish sooner, but fees or limits can apply. Fixed-rate restrictions and break costs deserve particular attention. An interest-saving estimate that leaves out a relevant fee overstates the benefit.
Why an 8% investment return does not automatically beat a 6% loan
A quoted investment return may be before fees, before tax, historical rather than prospective, or measured over a period unlike yours. It may include capital gains that cannot be spent without selling. A mortgage cost and an investment return need a consistent basis before comparing percentages.
Imagine a deliberately simplified investment that produces an 8% cash return, costs 0.5% in annual fees and has the remaining 7.5% fully taxed at an illustrative 32% rate. The after-tax return is 5.1%. On $10,000 that is $510, below the $600 simple loan-interest saving in the previous example.
This is a teaching example, not an Australian tax calculation. Actual distributions, deductions, capital gains, timing and tax rates differ. It shows why the word “return” must be unpacked. It does not establish the expected after-tax performance of shares, property or any specific product.
A break-even calculation is not a risk adjustment
Under that same simplified fully-taxed-return assumption, the gross return needed to match a 6% loan saving with a 0.5% fee is about 9.32%. The calculation is 6% divided by 0.68, then plus 0.5 percentage points. This only solves an arithmetic equality.
Even if an investment were expected to earn more than that, the outcome could be worse, particularly over a short period. A loan rate may also move. Comparing an uncertain investment outcome with a contractual interest cost requires more than choosing the larger percentage.
Ask what a loss would mean for the actual goal. If the money is needed for a known payment in two years, a large fall matters differently from a fall in money set aside for several decades. MoneySmart’s investing guidance emphasises time frame, risk tolerance and access to cash for this reason.
Use the same cash-flow budget on both paths
Suppose a household can allocate $500 each month. In one path, it pays that amount into the loan. In another, it invests the $500 while continuing normal loan repayments. A fair comparison tracks both the investment account and the remaining loan balance.
Do not compare the entire investment portfolio with only the interest saved on the loan. The extra mortgage repayments have also reduced the debt itself. Likewise, do not count the original $500 contributions as investment profits. Net wealth means considering the asset and liability sides together.
If the mortgage ends earlier under one path, state what happens to the freed repayments afterwards. Assuming they are invested in one path but spent in the other can overwhelm the result. The behaviour assumption belongs beside the financial assumptions, because real households may not automatically redirect every saved dollar.
Access and concentration can change the decision
A home can already represent a large part of household wealth. Paying more into it reduces debt but does not create a separate liquid investment portfolio. Investing elsewhere may spread exposure, depending on the underlying assets, but it also introduces market and product risks.
A household can reasonably value lower debt, accessible funds or a wider asset mix for different reasons. Write these priorities down instead of forcing them into an invented numerical score. A comparison that excludes all non-price preferences may be precise while still being unhelpful.
MoneySmart explains that diversification can reduce exposure to some investment risks. It does not promise that an alternative portfolio will perform well whenever the home falls in value. Check the actual exposures rather than assuming any second investment automatically creates useful diversification.
Rental-property and borrowed-investment cases need another analysis
The simple example assumes interest on an owner-occupied loan is not deductible. A loan used for income-producing purposes can have different tax treatment, and mixed-purpose borrowing creates additional record-keeping issues. Do not transfer the simple 6% comparison unchanged into an investment-property strategy.
Borrowing to invest also increases exposure: the debt remains even if the investment falls. This article does not assess leverage, debt recycling or whether an interest deduction is available. Those questions require the transaction history, purpose of the borrowing and current tax law.
MoneySmart’s investing-and-tax guidance explains that investment income and capital gains may affect a tax return. Use a registered tax agent for the tax assumptions, especially where announced reforms or changes in personal circumstances could affect a future outcome.
Source: MoneySmart: investing and tax
Build a decision you can review later
Record the amount, time horizon, loan conditions, accessible reserve and the investment assumptions. Run a lower-return case and a higher-loan-rate case without describing either as a forecast. Note what would make you reconsider: a job change, a fixed period ending or a near-term spending need.
Elaris’s monthly loan calculator can show the base repayment and a higher-rate scenario. It does not independently compare an investment strategy with extra mortgage payments, reproduce lender daily balances or calculate your tax. Use the output as one part of the worksheet, not a product recommendation.
If the result is close, uncertainty may matter more than the apparent lead. A difference of a few hundred dollars in a long projection can be overwhelmed by a fee, missed contribution or a small assumption change. Preserve that uncertainty in the decision record.
Test a loss without assuming you can simply wait
A fictional $10,000 investment falling 20% is worth $8,000 before costs. Recovering from $8,000 to $10,000 requires a 25% gain, not 20%. If the household needs to sell during the fall, the eventual recovery path may no longer matter to that goal.
Write down the date the money might be required and the consequence of having only $8,000 then. It might delay a discretionary purchase, or it might create a debt problem. Those are different risks even though the percentage fall is the same. This small stress test connects market uncertainty to the decision the money is meant to support.
FAQ: Is paying down the mortgage a guaranteed return?
Avoid treating that phrase as a universal promise. Extra payments generally reduce interest under the loan agreement, but the saving depends on rates, timing, fees and access arrangements. It is a reduction in borrowing cost, and its cash-flow effect can differ from an investment paying income.
FAQ: Should I split the extra money between both?
A split is another scenario to compare, not an automatic compromise that suits everyone. It may leave more accessible investments while reducing debt more slowly. Check whether either goal becomes underfunded and whether the additional accounts or transactions create costs.
FAQ: Does this change if I might rent the home out?
Potentially. The use of borrowed money, redraw history and future transactions can affect deductions. Obtain tax advice before moving a substantial amount rather than relying on what the property might later be used for. Offset and redraw should not be assumed identical.
FAQ: Which return should I put in a calculator?
Use a clearly labelled scenario that is consistent about tax and fees, then test less favourable assumptions. Do not enter a historical headline as a promised future return. If you cannot explain where the assumption comes from, the resulting payoff date deserves little confidence.
Put the next step into practice
Use your own confirmed figures and keep outstanding questions visible. Core tools are free, with no bank connection or compulsory account.
Open the Loan repayments ↗Sources and editorial notes
Sources checked 23 October 2026. Worked examples are fictional illustrations. Rules, eligibility and product terms can change; use the official source for your circumstances.
- MoneySmart: pay off your mortgage faster ↗
- MoneySmart: develop an investing plan ↗
- MoneySmart: investing and tax ↗
- MoneySmart: investment diversification ↗
General information, not an individual financial or legal assessment. AI-assisted drafting with source checks; independent professional review has not been completed. How we prepare our guides · Suggest a correction