Question 1

What is compound interest and how does it work?

Accepted Answer

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which only earns on the principal, compound interest earns interest on interest. This creates exponential growth over time — the longer you invest, the more dramatic the effect. For example, R10,000 at 10% annual compound interest becomes R25,937 after 10 years, not just R20,000 as simple interest would give.

Question 2

What is the difference between simple and compound interest?

Accepted Answer

Simple interest is calculated only on the original principal. If you invest R10,000 at 10% simple interest for 10 years, you earn R1,000 per year — R10,000 total interest. Compound interest earns interest on the principal plus all previously accumulated interest. The same R10,000 at 10% compounded annually grows to R25,937 — R15,937 in interest. The difference becomes more dramatic over longer periods and higher rates.

Question 3

How does compounding frequency affect returns?

Accepted Answer

More frequent compounding produces slightly higher returns because interest is added to the principal more often, creating a larger base for future interest calculations. For example, R10,000 at 10% for 10 years: annual compounding = R25,937; monthly compounding = R27,070. The difference grows with higher rates and longer periods. In practice, most savings accounts and fixed deposits in South Africa compound monthly.

Question 4

What is the rule of 72?

Accepted Answer

The rule of 72 is a quick mental math shortcut to estimate how long it takes to double your money. Simply divide 72 by the annual interest rate. For example: at 10%, your money doubles in approximately 72 ÷ 10 = 7.2 years. At 8%, it takes about 9 years. At 6%, about 12 years. It works for annual compounding and gives a reasonable approximation — the actual doubling time at 10% annual compounding is 7.27 years.

Question 5

How much will R10,000 grow in 10 years at 10%?

Accepted Answer

At 10% annual compounding, R10,000 grows to R25,937 after 10 years — that is R15,937 in pure interest, or a 159% total return. With monthly compounding at the same 10%, it grows to R27,070 — slightly more due to more frequent interest crediting. Adding a monthly contribution of R500 would grow the total to approximately R117,000, demonstrating the powerful combination of compounding and regular saving.

Question 6

What is a good interest rate for savings in South Africa?

Accepted Answer

In South Africa, typical savings rates vary by product: standard savings accounts offer 4–6%; money market accounts typically offer 7–9%; fixed deposits for 12+ months offer 8–11%; and tax-free savings accounts (TFSAs) offer similar rates with no tax on returns. Over the long term, a diversified equity portfolio has historically returned 10–15% annually. The South African Reserve Bank prime lending rate heavily influences these rates, so shop around regularly for the best available rates.

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Compound Interest Calculator South Africa 2026

Investment Growth Calculator

Investment Growth Summary

How to calculate compound interest

The Power of Compound Interest

Simple Interest vs Compound Interest

Real Example

The Rule of 72

Tips for Maximising Returns

Compound Interest Calculator — Frequently Asked Questions

Saving for yourself? In a tax-free savings account, the growth is not taxed.

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