See exactly how your savings grow over time
R500 per month. That's it. Invested consistently from age 25 at 10% annual return, R500/month grows to R2.85 million by age 65. The same R500/month started at 45 produces only R379,000 — seven times less from an identical monthly contribution. That is compound interest. Not a trick, not an optimistic assumption. Just maths — running for long enough.
This guide explains compound interest in plain terms, with real rand and dollar numbers, so you understand not just what it is but why it's the most important money concept most people are never taught properly.
Simple Interest vs Compound Interest: The Key Difference
Simple interest pays you the same amount every year on your original deposit. If you invest R10,000 at 10% simple interest, you earn R1,000 per year — every year. After 20 years you've earned R20,000 in interest. Your total is R30,000.
Compound interest pays you interest on your interest. In year 1 you earn R1,000 on R10,000. In year 2 you earn R1,100 on R11,000. In year 3 you earn R1,210 on R12,100. The earning base keeps growing — and by year 20 you're earning R6,116 in a single year on your original R10,000 investment. Total after 20 years: R67,275 versus R30,000 with simple interest. Same investment, same rate. The difference is R37,275.
| Year | Simple Interest Balance | Compound Interest Balance | Difference |
|---|---|---|---|
| Year 1 | R11,000 | R11,000 | R0 |
| Year 5 | R15,000 | R16,105 | R1,105 |
| Year 10 | R20,000 | R25,937 | R5,937 |
| Year 20 | R30,000 | R67,275 | R37,275 |
| Year 30 | R40,000 | R174,494 | R134,494 |
Why Starting Early Is Worth More Than Investing More
This is the most counterintuitive insight in personal finance, and the numbers are stark. Compare two investors:
Investor A starts at 25, invests R2,000/month until 35, then stops completely. Total invested: R240,000.
Investor B starts at 35, invests R2,000/month all the way to 65. Total invested: R720,000.
At 65, Investor A has more money. Despite investing R480,000 less. Because the 10 early years of compounding do more work than the 30 later years. This isn't a hypothetical — it's basic exponential maths. The implication: starting now, with whatever amount you have, beats waiting until you have more.
| Scenario | Monthly Investment | Years Invested | Total Invested | Balance at 65 (9%) |
|---|---|---|---|---|
| Start at 25, stop at 35 | R2,000 | 10 years | R240,000 | ~R4,100,000 |
| Start at 35, invest to 65 | R2,000 | 30 years | R720,000 | ~R3,340,000 |
| Start at 25, invest to 65 | R2,000 | 40 years | R960,000 | ~R7,400,000 |
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The SA Salary Trap — R149
The best way to maximise compound growth is to reduce your tax bill first. This guide shows SA employees how to legally keep more of their salary every month.
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