Consumer debt vs good debt

The usual definition is that good debt is cheap and consumer debt is expensive. That definition is wrong, or at least it is measuring the wrong thing, and it is why people talk themselves into interest-free plans that damage them anyway.

The distinction that holds up is narrower and much less flattering than the usual one:

• Good debt is a short, closed list: a mortgage on the home you live in, a HECS-HELP debt, and debt used to acquire a productive business asset. All three are attached to something that either holds value, raises your earning capacity, or generates income, and are structured, or chosen, so the cost is unusually low relative to what it buys.
• Consumer debt (debt for something that loses value) is everything else. Car loans, credit cards, personal loans, buy now pay later plans, interest-free store finance, money borrowed from family for a holiday. All of it, regardless of the rate.

Two clarifications, because this is where the usual definitions go soft.

Traditional student loans are not automatically good debt. HECS-HELP is unusual: it charges no interest, is indexed to inflation or wage growth (whichever is lower), and is only repaid once your income passes a threshold, so it cannot force a default. A commercial student loan or an overseas student loan has none of those features. Treat it by its actual interest rate, like any other debt, not by the word "education" attached to it.

An investment property mortgage is a different conversation, not an automatic pass. It sits on an appreciating asset, which is why the traditional definition lets it in, but it is also leverage (using borrowed money to invest bigger), and leverage magnifies a bad outcome exactly as much as a good one. Good debt here means the roof over your head, deliberately.

Notice what is absent from all of that: the interest rate. That is deliberate, and it is the whole point of this lesson.

Consumer debt with no interest at all

Every one of these is consumer debt (debt for something that loses value), with zero interest involved:

• Borrowing $3,000 from a friend for a holiday. No interest. No contract. Still consumer debt (debt for something that loses value).
• An interest-free buy now pay later plan, say an Afterpay or Zip Pay arrangement, for a $1,200 handbag you would not have bought with cash on hand.
• A 0% finance offer on a new phone. Whether the current one still works is irrelevant to why this is consumer debt.
• A family loan for a wedding that you otherwise couldn't afford.

None of those has an interest rate to object to, and every one of them still damages you. The reason is the one the previous lesson set out with the research behind it: having access to credit changes what you buy, independently of what the credit costs. The interest, where there is any, is the third problem on the list, not the first.

The two real costs, and interest is neither

First: it inflates what you spend beyond what you would have chosen in cash.

This is the cost almost nobody accounts for. Financing changes the question you ask yourself. With cash, the question is "do I want to hand over $65,000 right now". With finance, it becomes "can I handle about $620 a month". Those two questions produce different answers, and the second one reliably produces a bigger purchase.

The monthly framing is not a neutral way of presenting the same information. It is the entire sales mechanism. It is why cars are advertised by the week, why furniture is advertised in four instalments, and why nobody selling a $1,200 item leads with $1,200. A person shown $300 a fortnight and a person shown $1,200 are not evaluating the same proposition, even though they are.

Second: it permanently reduces your future disposable income.

Every repayment is a claim on money you have not earned yet. Zaid's roughly $620 a month is $620 of future disposable income (what's actually left over to save or invest) that is already committed, every month, for seven years, regardless of what else happens. That is about $7,430 a year, on a plan with no interest on it at all, and it is most of what he could otherwise be investing.

And it is rigid in a way that spending is not. If Zaid loses his job, he can cut groceries, cancel subscriptions and stop eating out. He cannot cut the car payment. Debt converts flexible spending into a fixed obligation, which is precisely the wrong direction to move when something goes wrong.

What the SUV actually cost, once you count everything

Put the two costs together and the shape of the decision becomes clear.

The first cost is the one above: the monthly framing is what made a $65,000 car feel like a sensible purchase when the question in cash would have been very different. Then the second cost lands: about $620 a month locked in for seven years, on an asset that is worth less every year. And then the third, which no statement will ever show him. The $52,000 he is handing over in instalments was also money that could have been invested. At the standard 10% assumption used throughout, $52,000 left to compound for seven years becomes about $101,000. So the true cost of the upgrade is not the sticker price. It is what he paid and what that money would have grown into, which is close to double.

Good debt, briefly

A closer look at the two items on that list that buy an asset: a mortgage on a property, and debt for a productive business asset, are structurally different from consumer debt because the thing being bought can grow in value or produce cash. That is what makes them capable of leaving you better off, though as the caveats below show, capable is not the same as guaranteed.

Two honest caveats, though.

Structurally capable is not the same as guaranteed. Borrowing to buy an appreciating asset is leverage (using borrowed money to invest bigger), and leverage magnifies the downside exactly as much as the upside. A property that falls in value while you owe money on it is a much worse outcome than one you owned outright. The same is true of borrowing for a business: it can fail, and the debt does not fail along with it.

And for a Muslim reader there is a larger problem than the label. The standard Australian version of good debt is an interest-bearing mortgage, and the good-debt category does not make interest permissible. So the honest position is that the largest item on the good-debt list, the home mortgage, is in its conventional form off the table, and the same is true of an interest-bearing business loan.

The Islamic version of the same idea: a partner instead of a lender

There is an alternative structure, and the logic of it is worth understanding here even though the detail belongs later. A conventional mortgage is a lender advancing money and being owed a fixed increase on it regardless of what happens to the house. The Islamic alternatives replace the lender with a partner.

The most common of them is Diminishing Musharakah (a co-ownership arrangement you buy your partner out of over time). You and the financier buy the property together as joint owners. You pay rent on the share you do not yet own, and separately buy that share out in instalments. As your share grows, the rent falls, until you own the whole thing. Nobody is lending money and charging for time. Two parties own an asset, and one of them is progressively buying out the other.

The substance of the difference is who carries the risk. A lender is owed its money whatever happens to the house. A co-owner owns part of the house, which means it is exposed to the house. Whether the products actually sold in Australia deliver that in practice, or whether the ownership step is largely paperwork, is a genuine and unresolved debate.

The structures available in Australia, the providers, the real costs and the scholarly dispute about whether they achieve what they claim are all in Islamic home finance alternatives, with the buy-versus-rent arithmetic in why people stick with mortgages. This lesson only makes the point that "good debt" has a risk-sharing equivalent, so the choice is not between an interest-bearing mortgage and renting forever.

The question to ask before borrowing

One question, and it works on every product including the interest-free ones:

Would I buy this, at this price, if I had to hand over the full amount in cash today?

If the answer is no, the finance is not helping you afford something. It is persuading you to buy something you had already decided against.