Do I buy another car or keep mine two more years?

You come back from the garage with a £750 quote and the sentence that sets everything off: “for what you’re about to spend, you may as well buy another one”.

It’s almost never true. But it sounds so good that a great many people change car at that moment, and not because of the sums.

The calculation almost nobody does

The right comparison isn’t repair against price of the new car. It’s this:

What it costs you per month to keep yours against what the other one would cost you per month.

With yours, per month:

• Today’s repair, spread over the months you expect it to last.
• Predictable maintenance for the next year.
• Insurance and tax, which you already pay.
• Depreciation (little: old cars have almost stopped falling).

With the other, per month:

• The price, spread over the years you’ll keep it.
• Depreciation, which in the early years is the largest cost of all and the one nobody writes down.
• New insurance, almost always more expensive.
• Tax, transfer, and whatever turns up in the first months.

When you put the two columns side by side, £750 spread over two years is about £31 a month. That rarely loses against the alternative.

When it genuinely is time to change

It isn’t all numbers. There are three good reasons and none of them is today’s quote:

When the expensive things fail. Engine, gearbox, structural corrosion. There you aren’t repairing: you’re buying time at a bad price.

When you no longer trust it. If the car leaves you stranded, or you think about breakdowns every time you head out on the motorway, that has a real value even if it doesn’t appear in the table. Especially if you depend on it for work or for carrying someone.

When what you need has changed. Different size, different seats, different use. That isn’t a fault, it’s that the car is no longer yours.

Notice that none of the three is “I’ve been given a big quote”.

The mental traps

Sunk cost. “I put new tyres on it recently” isn’t an argument for keeping it, and “I’ve already spent £1,700 this year” isn’t one for changing it. That money is gone. Only what happens from today counts.

Deciding on quote day. It’s the worst day to decide. Get the quote in writing, go home, decide another day.

Comparing against the car you fancy. You’re comparing a repair with a desire. Compare it with the car you’d actually buy, at its real price and its real insurance.

The questions that help

To the garage:

• “Is this safety, reliability or comfort?” (Only the first is urgent.)
• “What else will this car ask of me in the next 12 months, besides this?”
• “If it were yours, would you repair it or sell it?”

To yourself:

• How many months do I expect it to last after this repair?
• What’s it worth today if I sell it, repaired and unrepaired?
• If someone handed it to me fixed, would I still want it?

That last one unmasks a lot of decisions. If the answer is no, you weren’t deciding on money.

What asking an AI adds

Used well, it does two things that are hard to do alone in that moment:

The cold numbers. Give it the details — age, mileage, quote, what your car is worth, what the other would cost — and ask for both columns per month. No enthusiasm and no nostalgia.

What you’re not looking at. “What am I not taking into account in this decision?” It usually brings one or two things: first-year depreciation, pricier insurance, or that in two years you’ll need something different.

And more than one opinion helps here for a specific reason: on decisions like this, a single AI tends to give you a tidy answer, and this decision isn’t tidy. When several agree that the sums favour repairing but differ on the “yes, but”, that “but” is exactly what you need to look at.

What usually happens

In most cases with older cars, repairing wins clearly — until the car starts asking for several things a year, and then the picture changes.

The signal isn’t the size of one invoice. It’s the frequency.