If you've got spare cash and want it working to reduce your mortgage interest, you generally have two options: pay it directly off your loan as an extra repayment, or park it in an offset account. Both reduce the interest you're charged by roughly the same amount. The real difference is what happens to that money afterwards, and how easily you can get it back.
Extra repayments: locked in, but not always gone
Paying extra off your mortgage reduces your loan balance directly, and interest is calculated on that lower balance from that point on. It's a straightforward, disciplined way to pay off your home sooner. The catch is accessibility: getting that money back later means using your loan's redraw facility, which some lenders limit, charge fees for, or restrict during periods of financial hardship or if you refinance. Extra repayments suit borrowers who want a set-and-forget approach and are unlikely to need the money again before the loan is paid off.
Offset accounts: same benefit, full flexibility
Money sitting in an offset account reduces the interest you're charged in exactly the same way, since the bank calculates interest on your loan balance minus your offset balance. But that money never actually leaves your hands. It sits in an everyday account with a debit card and full access, so you can spend or transfer it any time without needing to apply for a redraw. Your minimum required repayment also stays the same as if you had no offset at all, meaning more of every repayment goes toward the principal automatically.
Why the "same interest saving" claim actually holds up
Because both options reduce the balance interest is calculated on by the same amount, the interest saved is effectively identical for a given amount of money, whether it sits in an offset account or gets paid directly onto the loan. The difference is entirely about access and flexibility, not about which one saves you more in interest.
So which one is right for you?
If you want the money to stay easily accessible, for emergencies, opportunities, or just peace of mind, an offset account is usually the better fit. If you know you won't need the money and want the certainty of a shrinking loan balance with less temptation to spend it, extra repayments can work well, provided your loan allows redraw without excessive fees or restrictions in case your circumstances change. Many households use both: keeping three to six months of expenses in an offset account as a buffer, then directing any additional surplus into extra repayments.
This is general information only. Everyone's income, expenses, and risk tolerance are different, so if you're unsure which approach suits you, it's worth speaking with a financial adviser or mortgage broker who can look at your full situation.