Using your home loan to buy a car — what you're actually trading

The question usually arrives in the same shape. "I've got the money sitting in my offset. Should I just use it for the car, or get a car loan?"

It's a fair question, and it's almost always asked as a question about rate. The home loan is at one number, the car loan is at a higher number, so the home loan must be the cheaper way to pay for it. End of analysis.

If that's where your thinking has landed, that's normal. Rate is the one figure that's printed on everything. But when you look at how these options actually play out over the life of a car and the life of a mortgage, rate turns out to be the least important of four things you're trading. The other three are quieter, and they're the ones that tend to matter later.

Interest rate. The visible one. A home loan rate is lower than a car loan rate. True, and worth knowing. But a rate only tells you the price per year. It doesn't tell you how many years you'll be paying it.

Loan term. This is the part most people don't see. A car is a depreciating asset. A new one is commonly worth around half its purchase price after five years. A home loan runs on a 25 or 30-year schedule. Put the car inside the home loan without doing anything else, and you're paying a low rate on a vehicle for long after it's been sold, scrapped or replaced. A lower rate over a much longer term can cost more in total than a higher rate over a shorter one.

Liquidity. Cash you can get to tomorrow is worth something, and it's worth more in a bad month than a good one. Some of these options keep your buffer intact. Some of them spend it.

Your next lending decision. Lenders assess a new application on what you owe and what you pay each month. A car funded one way shows up as a new liability on that assessment. Funded another way, it doesn't show up at all. If there's a property purchase somewhere in your future, this variable can outweigh the other three combined.

With those four in view, here's how each option looks.

The simplest option, and the one with the least paperwork. You transfer the money out and buy the car.

The cost is real but easy to miss, because nothing new appears on a statement. Every dollar in your offset was saving you interest at your home loan rate. Take it out and that saving stops. So the effective cost of this option is your home loan rate, applied to the money you've withdrawn, for as long as it stays out.

What you get in return is clean. No application, no serviceability assessment, no credit enquiry, no new liability. On a future lending application there is nothing to disclose, because nothing was borrowed.

What you give up is the buffer. That offset balance was doing two jobs: reducing interest, and sitting there in case something went wrong. The car spends both. And for an owner-occupier, none of this changes your tax position either way, because interest on a loan for your own home isn't deductible regardless of what's in the offset.

Most people treat redraw and offset as two names for the same thing. On a normal day they behave the same way, which is why the assumption sticks. But they are structurally different, and the difference shows up at exactly the moments you'd want it not to.

Money in an offset is yours. It sits in an account in your name, and the bank calculates interest as if it had been paid off the loan. Money in redraw is the lender's. You paid it ahead of schedule, and the lender lets you take it back out as a courtesy under the loan contract. Most contracts let the lender limit or suspend that access, and some have done so when borrowers fell behind or when conditions changed.

The second difference is quieter and only matters if the property ever becomes an investment. When you redraw to buy a car, you've increased the loan balance, and that extra borrowing was used for a private purpose. The loan is now part property, part car. If you later rent the place out, the interest on the car portion isn't deductible, and separating the two for the rest of the loan's life is a bookkeeping exercise most people would rather not have. Drawing the same amount from an offset doesn't touch the loan balance at all, so the loan's original purpose stays intact.

For someone who will live in the property until they sell it, this may never matter. For someone who might keep it as an investment one day, it's worth understanding before the transfer, not after.

This is the option that wins on rate. You borrow against the property, at the home loan rate, and the offset stays where it is.

It is also a full application. The lender assesses your income and commitments again, runs a credit enquiry, and may order a valuation. If anything has changed since you last applied, such as income, a new child, or a card limit, you'll find out here.

The larger issue is the term. Borrow an extra $30,000 on a loan with 28 years to run, and by default that $30,000 is on a 28-year schedule. The monthly repayment looks small, which is the trap. A low rate stretched across three decades on an asset that's worth little after one is not cheap.

There's a disciplined version. Set the top-up up as its own split, and treat it as a five-year loan, making repayments at the level that would clear it in that time. You get the home loan rate with a term that matches the car. It only works if the extra repayments actually happen, and nothing in the loan contract makes you do it.

A higher rate than the home loan, on a five to seven-year term that roughly matches how long the car will be useful. The offset stays intact. The debt ends when the car's working life does, without you having to impose that discipline yourself.

The hidden cost sits on your next application. The loan is a new liability and a new credit enquiry, and lenders assess your future borrowing capacity on your commitments at the time you apply.

As an illustration, a $30,000 car loan over five years at a typical rate works out to around $600 a month. On a home loan application, that monthly commitment reduces how much you can borrow by a figure in the tens of thousands. At the kind of assessment rate lenders are required to test against, which sits well above the rate you'd actually pay, something in the region of $70,000 is a reasonable order of magnitude. The exact number depends on the lender and your situation. The direction doesn't.

Two practical limits worth knowing. Many asset lenders restrict the age of the vehicle at the end of the term, so an older car may not qualify or may be priced higher. And a private sale, rather than a dealer purchase, is treated differently by some lenders and excluded by others.

This one is only available to PAYG employees whose employer offers it. The car is leased, and the repayments and running costs come out of your salary, with part of that taken before tax. Because of the tax treatment, the cash cost of a novated lease can come in below every other option on this list, particularly for higher earners and for electric vehicles that qualify for the fringe benefits tax exemption.

What you're trading is flexibility. It's a contract tied to your employment. Change jobs and the arrangement has to be unwound or carried across, which isn't always smooth. There's usually a balloon payment at the end, and lenders will still count the lease as a commitment when you next apply for a home loan. It's worth running the numbers properly rather than taking the packaging provider's figures at face value.

A very low headline rate on a new car is rarely free money. It's usually funded by a less negotiable purchase price, so the saving on interest is often given back on the sticker. It also tends to apply only to new or near-new vehicles bought through the dealer, so it isn't on the table for a used car from a private seller. If you're comparing it against the options above, compare the total you'll pay for the car, not the rate on the brochure.

What actually matters here is not which option is cheapest in isolation. It's what else you're planning to do with your borrowing capacity.

If a property purchase is likely in the next six to twelve months, a new liability lands at the worst possible time. The car loan shows up on the application, the repayment is counted against you, and the number you can borrow drops. Using cash from the offset instead reduces your deposit, which is a cost, but it leaves your capacity untouched. In that situation, the lowest-rate option on paper can be the most expensive one in practice, because it costs you part of the next purchase.

If there's no lending event ahead, the picture turns around. With nothing to protect, liquidity moves to the front. Keeping your offset intact and letting the car carry its own debt starts to look sensible, even at a higher rate, because the buffer stays available for whatever comes next.

Neither of those is a verdict. They're the same four variables, weighted differently by what's coming.

One scenario simplifies things. If the home is going to be sold in the foreseeable future, any car debt that was added to the home loan, whether by redraw or top-up, is cleared from the sale proceeds at settlement. In effect, the car is paid for in cash either way. The only difference is whether that cash leaves your hands now or later, and what the interest on it cost in between.

Rate, term, liquidity, and your next lending decision. Every option on this list wins on at least one of those and gives something up on another. The offset is cheap and clean but spends your buffer. Redraw looks like the offset until the day it doesn't. A top-up has the best rate and the worst default term. A car loan matches the asset and protects the buffer, then takes a bite out of your next application. A novated lease can beat all of them on cash cost and ties you to your employer.

The right option is whichever one costs the least across all four, for your situation and your timing. It's rarely the one with the lowest rate, and it's worth working that out before the money moves.