Is Financing Your Car on Your Mortgage Actually Costing You More?
A lower interest rate doesn't always mean a cheaper loan.
When you're buying a vehicle and you already own a home, putting the car onto the mortgage can seem like the obvious choice.
After all, if your mortgage rate is around 5.40% and vehicle finance is around 8.45%, why would you choose the higher rate?
Because there's another number that's just as important as the interest rate:
The term.
And this is where a seemingly cheaper way of borrowing can become surprisingly expensive.
Let's Compare a $50,000 Vehicle
For this example, let's assume you're financing $50,000.
Option 1: Add $50,000 to the mortgage
Interest rate: 5.40%
Term: 20 years
Approximate monthly repayment: $341
Approximate total repaid: $81,870
Approximate interest paid: $31,870
Option 2: Vehicle finance
Interest rate: 8.45%
Term: 5 years
Approximate monthly repayment: $1,025
Approximate total repaid: $61,477
Approximate interest paid: $11,477
The difference?
Despite the vehicle finance having the higher interest rate, in this simplified example the mortgage option could cost approximately:
$20,393 MORE in interest.
Why?
Because you're paying interest on that vehicle debt for 20 years instead of five.
Figures are illustrative estimates only, based on principal-and-interest monthly repayments with no fees and an unchanged interest rate for the full term. Actual mortgage and vehicle finance rates, fees, repayment structures and costs will vary.
The Question Isn't Just "What's the Interest Rate?"
This is one of the biggest things I encourage people to look at when comparing finance.
Don't just ask: "What's the rate?"
Ask: "How much will this actually cost me, and how long will I be paying for it?"
A lower rate stretched over a much longer period can potentially cost considerably more than a higher rate paid off quickly.
There's also something slightly uncomfortable about the idea of still paying for today's vehicle in 15 or 20 years' time — potentially long after you've sold or traded it.
But What If I Put the Car on My Mortgage and Pay It Off in Five Years?
Now we're having a very different conversation.
If the $50,000 were borrowed at 5.40% and genuinely repaid over five years, the approximate numbers would be:
Monthly repayment: $953
Total repaid: $57,165
Total interest: $7,165
In that scenario, the lower mortgage rate can absolutely work in your favour.
That's why I don't think the answer is: "Never put a car on the mortgage."
The better answer is: Understand the structure.
If you use your mortgage to fund a vehicle, consider separating that borrowing and setting the repayments so the vehicle portion is cleared over a realistic vehicle ownership timeframe — rather than simply absorbing it into a 20- or 30-year home loan.
What If Cash Flow Is the Reason You're Considering the Mortgage?
This is where it gets interesting.
Often the attraction of putting a vehicle on the mortgage isn't really the interest rate.
It's the lower repayment.
You might comfortably afford the vehicle overall but not want another large monthly or fortnightly commitment.
In that situation, it may be worth considering whether vehicle finance with a balloon payment could provide another option.
A balloon payment is an agreed amount left owing at the end of the finance term.
Because you're not paying the entire principal down through your regular repayments, your repayments during the term are lower.
For example, using the same illustrative $50,000 vehicle, financed over five years at 8.45%, with a $20,000 balloon:
Approximate monthly repayment: $756
Balloon at the end: $20,000
Approximate total interest: $15,336
That's higher than financing the entire $50,000 over five years with no balloon, because you're carrying more debt for longer.
But the monthly repayment is also approximately $269 lower.
That can provide a middle ground for someone who wants to manage cash flow without automatically stretching the vehicle debt across decades.
At the end of the term, depending on your circumstances and the finance agreement, you may choose to pay the balloon, refinance it, or sell/trade the vehicle and use the proceeds toward the outstanding amount.
The important thing is to plan for the balloon from day one — it isn't free money, and it doesn't disappear.
Already have vehicle finance or a balloon payment coming up? Read my guide to whether it could be time to refinance your vehicle.
There's Another Difference: What Is Securing the Debt?
This is something I think deserves more attention.
With traditional secured vehicle finance, the vehicle will commonly be security for the loan.
When borrowing through your home loan, your property secures the mortgage borrowing.
That doesn't automatically make one option good or bad.
But they're not the same thing, and it's worth understanding what you're putting behind the debt before making the decision.
Don't Forget Depreciation
Most everyday vehicles are depreciating assets.
That's another reason I'm cautious about simply spreading a vehicle purchase over a very long mortgage term.
Imagine buying a $50,000 vehicle today.
Several years from now you may want to trade it for another vehicle.
If the original vehicle debt has simply disappeared into the mortgage rather than being deliberately paid down, you could potentially add the next vehicle to the mortgage too.
Then another one later.
Over time, it becomes difficult to tell how much of the mortgage is actually paying for the house — and how much relates to vehicles you no longer own.
So Which Option Is Better?
There isn't one answer that suits everyone.
The right structure depends on things like:
how long you expect to keep the vehicle
your available deposit or trade-in
your cash flow
the interest rates available to you
the term of the borrowing
whether a balloon is appropriate
fees and early repayment costs
what asset is securing the debt
and, most importantly, the total cost of borrowing
Sometimes using the mortgage may make perfect sense — particularly if you're disciplined about paying the vehicle portion off quickly.
Sometimes dedicated vehicle finance may be the better fit.
And sometimes a balloon structure can give you the cash-flow flexibility you're looking for without turning a five-year vehicle purchase into 20 years of debt.
Buying for your business? The numbers can look different again. Read my guide to financing a vehicle for your business.
Before You Put Your Next Car on the Mortgage...
Run both sets of numbers.
Don't compare 5.40% versus 8.45% and stop there.
Compare: Rate + Term + Repayment + Balloon + Fees + Total Interest + Total Amount Repayable.
That's the comparison that tells you what you're really paying.
Want Me to Run the Numbers?
If you're considering a new vehicle — or you've already put a vehicle on your mortgage and you're wondering whether there's another way to structure it — I'm happy to help you compare the options.
I can look at the vehicle price, deposit or trade-in, preferred repayment, finance term and potential balloon and show you what different structures could look like.
No guesswork. Just the numbers, side by side.
Adrianne Drives Smarter | Smart Money Motoring
Helping Kiwis fund, protect and enjoy their vehicles — one conversation at a time.
This article provides general information only and isn't personalised financial advice. Finance is subject to lender criteria, affordability assessment, terms and conditions. Interest rates and fees vary. Consider your circumstances and seek independent financial advice where appropriate.
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