It’s one of the most common money questions we’re asked, and it almost always arrives wrapped in emotion. Debt feels like a weight you want gone. Paying it down feels responsible. Investing feels like progress. So when there’s money left over at the end of the month, which one deserves it?
Strip away the feeling and it becomes an arithmetic question with a surprisingly clean answer. Paying down debt earns you a guaranteed, tax-free return equal to the interest rate on that debt. Investing offers a higher possible return, but an uncertain one. The entire decision turns on comparing those two numbers: the rate on your debt against the return you can realistically expect, after tax, from investing instead.
This guide works through both sides, gives you a simple framework for deciding, and covers the South African specifics that quietly change the answer. It builds on the foundations of compound interest and debt — if you haven’t read that, it’s a useful place to start.
Key Definitions
Hurdle rate
The return your investments would need to beat for investing to make more sense than repaying debt. It’s simply the interest rate on the debt, because that’s the return you lock in by paying it off.
Guaranteed return
Paying down debt is one of the only places you earn a known, risk-free, tax-free return. Reducing a 10.5% loan is the equivalent of earning 10.5% with certainty — no market can promise that.
After-tax return
The return on an investment once tax on growth or income is accounted for. It’s the number that should be compared to a debt rate, not the headline return, unless the investment sits inside a tax-free wrapper.
Good debt vs bad debt
Good debt funds an appreciating asset or future earning power at a manageable rate; bad debt funds consumption at a high one. The interest rate and what the money bought matter more than the borrowing itself.
Opportunity cost
What you give up by choosing one option over the other — here, either the interest you keep paying, or the compounding growth you forgo by not investing early.
The Real Question Is the Interest Rate
The debate is usually framed as a clash of virtues: discipline versus ambition, safety versus growth. It isn’t. It’s a comparison between two returns. Paying off a debt gives you a guaranteed return equal to its interest rate. Investing offers a return that might be higher, but isn’t promised. Whichever number is larger, on a risk-adjusted basis, wins.
That single idea does most of the work. A debt charging 20% is a 20% guaranteed, tax-free return waiting to be claimed. No sensible investment strategy reliably beats that, so the choice makes itself. A home loan at 10.5%, against a long-term portfolio that might earn more over decades, is a genuinely close call. The interest rate is the hurdle, and the hurdle decides.
| Dimension | Paying off debt | Investing |
|---|---|---|
| Return | Guaranteed, equal to the interest rate | Potentially higher, not guaranteed |
| Certainty | Certain | Variable — depends on markets |
| Tax | Effectively tax-free | Often taxed, unless held in a TFSA or RA |
| Access to the money | Gone, unless you use an access facility | Stays accessible (in a discretionary investment) |
| Best when | The debt rate is high | Expected after-tax return comfortably beats the debt rate |
For context, South African lending is priced off the prime rate, currently 10.5% (prime sits 3.5 percentage points above the Reserve Bank’s repo rate of 7.0%). That’s the reference point for the rest of this discussion.
The Case for Paying Off Debt First
The argument for clearing debt is its certainty. Markets can disappoint for years at a stretch; a 20% credit card charges you 20% every single year, without fail. Removing that cost is the closest thing to a risk-free, tax-free return you’ll ever find, and it shows up immediately in your cash flow rather than someday on a statement.
This is decisive for expensive debt. The numbers aren’t close:
| Debt type | Typical rate (illustrative) | Lean |
|---|---|---|
| Credit cards, store and retail accounts | ~18% to 22%+ | Pay off first — almost always |
| Unsecured personal loans | Often above 20% | Pay off first |
| Vehicle finance | ~Prime to prime + 2% (≈10.5%–12.5%) | Usually pay down |
| Home loan (primary residence) | ~Prime (≈10.5%) | A close call — see below |
To make investing worthwhile instead of clearing a 20% card, you’d need a reliable after-tax return north of 20%. That doesn’t exist without taking wild risk, which rather defeats the point. Carrying expensive debt while investing your spare cash is, in most cases, paying 20% to chase 9%. The arithmetic simply doesn’t work.
The Case for Investing Instead
The case for investing strengthens as the debt rate falls and your time horizon lengthens. A diversified growth portfolio has, over long periods, delivered returns ahead of typical secured-debt rates. If your debt costs 8% and your realistic long-term return is higher after tax, investing can leave you better off — and crucially, you keep your money working and accessible rather than sunk into a loan.
Two things tilt the maths further toward investing. The first is tax. Inside a tax-free savings account, growth and income are sheltered entirely; inside a retirement annuity, contributions earn an immediate tax deduction and grow tax-free. A deduction at a 45% marginal rate is effectively an instant, guaranteed return that very few debts can match — though the money is then locked away until retirement. The second is time. The compounding you forgo by delaying investing is rarely recovered, because the earliest contributions are the ones with the longest runway to grow.
The honest qualifier: investing only wins if you actually invest. A surplus earmarked for the market that quietly drains into lifestyle spending delivers a return of zero, while the debt keeps compounding against you. The strategy is only as good as the discipline behind it.
A Simple Framework for Deciding
Rather than agonise case by case, work through four steps in order.
1. Build a baseline emergency buffer first. Before aggressively doing either, hold enough accessible cash to cover three to six months of essentials. Without it, an unexpected expense pushes you straight back onto expensive credit, undoing the progress.
2. Clear high-interest debt, always. Anything above roughly 12% to 15% — cards, store accounts, unsecured loans — comes first. The guaranteed return from eliminating it beats any realistic after-tax investment return.
3. For low-rate debt, compare the two returns honestly. This is where the home loan lives. Consider R200,000 in spare cash against a bond at 10.5%. Paying it down earns a certain, tax-free 10.5% and shortens the loan. Investing it in a growth portfolio at an assumed 9% (illustrative, before tax) offers more upside over twenty years but no guarantee, and the return may be taxed outside a wrapper. On those numbers, the bond is genuinely competitive — which surprises people who assume investing always wins.
4. Don’t sacrifice the tax wrappers. Maxing your annual TFSA and RA contributions is usually worth protecting even while paying down low-rate debt, because the tax benefit and tax-free compounding are hard to replicate later. The contribution room doesn’t carry forward in the same way the debt does.
One South African detail matters here. Interest on a loan against your primary residence is not tax-deductible, so paying down your bond delivers a clean, tax-free 10.5% equivalent. (Interest on a buy-to-let property is deductible against rental income, which changes that calculation.) It’s a small point that meaningfully strengthens the case for attacking the home loan rather than assuming the market will do better.
Beyond the Numbers
The arithmetic sets the boundaries; temperament decides within them. Some people sleep better with a smaller bond and will happily accept a slightly lower expected outcome for that peace of mind. That’s a legitimate choice, not a mistake, provided it’s made knowingly.
Liquidity is the other consideration. Money paid into a flexible access bond can often be drawn back out if needed, which softens the usual objection that repaying debt locks your cash away. Money inside a retirement annuity, by contrast, is genuinely inaccessible until retirement. And variable rates cut both ways: today’s 10.5% bond could be cheaper or dearer in two years, while a fixed-rate debt gives you certainty to plan around.
In practice, the answer for many people isn’t one or the other. Splitting a surplus — part to the bond, part to a tax-free investment — captures some guaranteed saving, some market upside, and some liquidity, while keeping the discipline of doing something deliberate with the money. The worst outcome is usually indecision, where the surplus simply evaporates.
Frequently Asked Questions
Should I pay off my home loan or invest?
It's the closest call of all the debt types. Paying down a bond at around prime (currently 10.5%) gives a guaranteed, tax-free return, since home-loan interest on your primary residence isn't tax-deductible. Investing may beat that over a long horizon but isn't guaranteed. Many people sensibly split their surplus between the two.
Is it worth investing while I have credit card debt?
Almost never. A credit card charging around 20% is costing you a guaranteed 20% a year. No reliable investment beats that, so clearing the card is effectively a risk-free 20% return. Pay off expensive debt first, then invest the freed-up cash flow.
Does paying off debt really count as a "return"?
Yes. Every rand of interest you no longer pay is a rand you keep, with certainty and no tax. Reducing a 10.5% loan is financially equivalent to earning a guaranteed, tax-free 10.5% — which is why the debt's interest rate is the hurdle any investment has to clear.
Should I stop my retirement contributions to pay off debt faster?
Usually not. Retirement fund contributions earn an immediate tax deduction and grow tax-free, a benefit that's hard to recreate later and that few debts can match. The exception is genuinely expensive debt in a cash-flow crisis, where clearing it briefly may take priority. For most low-rate debt, keep contributing.
What interest rate is high enough that I should always pay it off first?
As a rule of thumb, debt costing more than your realistic long-term after-tax investment return — broadly above 12% to 15% in the current environment — should be cleared before investing. That captures cards, store accounts, and most unsecured loans. Below that, it becomes a genuine comparison.
The Hurdle Is the Whole Answer
For all the emotion the question carries, the decision rests on one comparison: the guaranteed return from clearing a debt against the uncertain return from investing instead. The debt’s interest rate is the hurdle, and most of the time it tells you plainly what to do.
Clear expensive debt before anything else — the maths isn’t close. Treat the home loan as the genuine judgement call it is, decided by your time horizon, your appetite for uncertainty, and whether you’ll use your tax wrappers. And whatever you choose, protect the tax-free compounding inside a TFSA or RA, because that advantage is difficult to win back later.
If you’d like to see how this fits your own numbers — your debt rates, your tax position, and a realistic return assumption — that’s exactly the kind of trade-off we model with clients. It also sits within the broader picture covered in our guide to financial planning fundamentals.
This article is for informational purposes only and does not constitute financial advice. Henceforward (Pty) Limited is an authorised representative of Graviton Wealth Management (FSP 8772). References to market events and historical performance are for illustrative purposes only and are not indicative of future results. Projections and illustrations are for discussion purposes only. Consult a qualified financial advisor before making any investment decisions.