Compound Interest Calculator — South Africa
Project how your savings grow with compound interest, full SA tax treatment applied — including annual interest exemptions.
Last updated: May 2026
Your Details
Enter as decimal — e.g. 0.085 for 8.5%
Interest exemption: R23,800/year
Enter your details and click Calculate
Results show your projected growth with SA interest tax treatment applied year by year.
Calculates how an investment grows when interest earned is reinvested — so you earn interest on your interest. The longer the term, the more dramatic the effect.
Key inputs explained
- Principal
- Your starting investment amount.
- Monthly contribution
- Regular additions to the investment — even small amounts compound significantly over time.
- Annual rate
- Expected annual return before fees and inflation.
- Compounding frequency
- More frequent compounding (monthly vs annually) produces slightly higher returns.
At 10% annual return, money doubles roughly every 7.2 years (the Rule of 72). Starting 10 years earlier can more than double your final amount.
Frequently Asked Questions
The Rule of 72 is a quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8% per year, your money doubles in approximately 9 years (72 ÷ 8). At 10%, it doubles in about 7.2 years. The rule works well for rates between 6% and 15%.
Compounding frequency does matter, but the real power of compound interest comes from the rate and the time, not whether it compounds monthly vs daily. The difference between monthly and daily compounding on R100,000 at 8% over 10 years is less than R500.
The nominal rate is the stated annual rate. The effective annual rate (EAR) is the actual return after accounting for compounding frequency. For example, 10% nominal compounded monthly gives an EAR of 10.47%. SA banks are required to disclose the effective rate (NACM or NACC) under the National Credit Act.
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