Albert Einstein is often credited with calling compound interest the eighth wonder of the world. Whether or not he actually said it, anyone who has watched a retirement fund grow over several decades understands exactly what the quote is getting at.
When clients ask me what the single biggest lever is in retirement planning, they usually expect me to talk about fund choice, asset allocation or market timing. The honest answer is far less exciting, and far more powerful: time.
The mechanics, in plain terms
Compound interest is simply interest earned on interest. Your initial contribution grows, and then the growth itself starts generating growth. In the early years the effect is barely noticeable.
Given enough time, it becomes the single biggest driver of your final retirement value, often outweighing the amount you actually contributed.
Consider a once-off investment of R10 000 growing at 9% a year, with nothing added and nothing withdrawn:
| Years invested | Value | Growth from compounding |
|---|---|---|
| 10 years | R23 674 | R13 674 |
| 20 years | R56 044 | R46 044 |
| 30 years | R132 677 | R122 677 |
| 40 years | R314 094 | R304 094 |
| Assumptions: Once-off R10 000 investment at an illustrative 9% a year, with no further contributions and no withdrawals. | ||
Notice how the curve steepens. The jump from year 30 to year 40 is larger than the entire value at year 30. That is compounding doing the heavy lifting, and it is entirely dependent on one input you control completely: how early you start.
The ten-year gap
Here is where it becomes personal, and where retirement fund contributions specifically come into play.
Consider two clients, both contributing R2 000 a month to a retirement annuity, both earning an illustrative 9% average annual return, and both retiring at 65. The only difference between them is when they started.
| Client | Years contributing | Value at 65 |
|---|---|---|
| Starts at 25 | 40 years | R9 362 641 |
| Starts at 35 | 30 years | R3 661 487 |
| Assumptions: R2 000 contributed monthly at an illustrative 9% average annual return, with retirement at age 65. | ||
The client who started at 25 contributed R240 000 more over their working life than the client who started at 35, roughly ten extra years of R2 000 monthly contributions. For that additional R240 000, they ended up with more than R5.7 million more at retirement.
That gap is not a product choice, a market call or a stroke of luck. It is purely the cost of waiting.
These figures are for illustration only. Actual returns will vary from year to year and are never guaranteed, but the underlying principle holds regardless of the exact growth rate used.
Why this matters more inside a retirement fund
Retirement annuity and pension fund contributions carry an additional advantage that ordinary investing does not: they are tax deductible, up to 27.5% of your taxable income, capped at R430 000 a year. A portion of every contribution that would otherwise have gone to SARS is instead working for you inside the fund, compounding alongside the rest of your capital.
Since September 2024, South Africa’s two-pot retirement system has also changed the shape of this conversation. Two-thirds of every new contribution goes into a preservation component that cannot be accessed before retirement, while one-third goes into a savings component available for emergencies.
The preservation component matters here because it protects the very thing compounding needs most: an uninterrupted runway.
Every early withdrawal does not just reduce your capital, it resets part of the clock on the growth that capital would otherwise have generated.
What this means for you
If you are years away from retirement, the temptation is to believe that the real work of retirement planning happens closer to the date, once the numbers feel more urgent. The maths says the opposite. The single most valuable retirement planning decision most people can make is the one available to them today: start now, contribute consistently, and let time do the rest.
If you have already started, resist the urge to interrupt it. The two-pot system aside, every withdrawal from a retirement fund before retirement age doesn’t just draw down capital, it draws down decades of future compounding on that capital.
Compound interest rewards patience more reliably than it rewards almost anything else in investing. The best time to start was ten years ago. The second best time is today.
