Paying off debt vs investing: which comes first?

Part of Investing foundations

It’s one of the first money crossroads everyone hits: a bit of spare cash, and a choice between paying down what you owe or putting it to work. A single idea makes the whole thing clearer.

The idea that makes it simple

Here’s the unlock: paying off a debt is a certain return. If a card charges you 18% a year and you clear it, you’ve just ‘earned’ a certain 18% — that’s interest you will now never pay, whatever the markets do. Investing, by contrast, might earn more over time, but the outcome is uncertain and can be negative in any given year. So the real question is: is the certain return from clearing this debt better than an uncertain one from investing?

Why expensive debt usually comes first

Put that way, high-interest debt is an easy call for most people. Credit cards, overdrafts and payday-style loans often charge far more than a diversified portfolio can reliably be expected to return — so clearing them is like locking in a high, certain gain that beats an uncertain, lower one. There’s a reason ‘pay off the expensive stuff first’ is one of the few things almost everyone in personal finance agrees on. It’s money you’re sure to keep, and it’s usually a lot.

Low-interest debt is a genuine toss-up

It gets more interesting with cheap debt — say a long mortgage at a modest rate. If the rate is lower than markets have historically tended to return, some people happily invest alongside the debt, betting the portfolio out-earns the interest over decades. Others simply loathe owing money and clear it for the peace of mind, accepting they might leave some theoretical gains on the table. Neither is wrong: it’s part arithmetic, part temperament, and both are perfectly reasonable.

It’s rarely all-or-nothing

In practice plenty of people do a bit of both — chipping at a cheap debt while also investing a little, so they build the habit and the balance together. Most also keep a cash buffer for emergencies no matter what, so a surprise bill doesn’t send them back to the expensive borrowing they just escaped. What fits depends on your interest rates, your job security and how you feel about debt — this is a way to think it through, not advice on your particular choice.

Common questions

Should I stop investing entirely until all my debt is gone?

Not necessarily — it depends on the debt. Expensive debt (cards, overdrafts) is where the ‘clear it first’ logic is strongest, because the certain saving is large. Cheap, low-rate debt is more of a personal call, and some people invest alongside it. This is a framework, not advice.

What counts as ‘expensive’ debt?

There’s no official line, but the higher the interest rate, the stronger the case for clearing it before investing — because the certain saving from repaying it is that much bigger. Double-digit rates (typical of cards and overdrafts) are the classic ‘pay this first’ territory; low single-digit rates are where it becomes a genuine judgement call.