Compound interest calculator

See how your money grows with compound interest, monthly contributions and an annual increase. You also see the result in today's rands, after inflation.

Starting amount (R)

Monthly contribution (R)

Yearly increase (%)Raise your monthly amount each year, e.g. with your salary.

Annual return (%)

Years

Inflation (% per year)

What is compound interest?

Compound interest is interest earned on your interest. At 10% a year, R10 000 becomes R11 000 after one year, then R12 100 after two. The growth speeds up over time, which is why starting early matters more than starting big.

Why increase contributions every year?

Raising your debit order with each salary increase (say 5–6% a year) keeps your savings up with inflation and makes a big difference over 20+ years. Try setting the yearly increase to 0% to compare.

Why show the result after inflation?

R1 million in 20 years won't buy what R1 million buys today. The "in today's rands" figure discounts your result by inflation so you can see its real buying power.

How the calculation works

The annual return is converted to an equivalent monthly rate: (1 + annual rate)^1/12 − 1. Each month the balance grows by that rate and your contribution is added. Each year the contribution rises by your chosen increase. Finally, the result is divided by (1 + inflation)^years to show it in today's rands.

Worked example: R1 000 a month for 20 years

Start with R10 000 and save R1 000 a month, increasing it by 5% each year.
At a 10% annual return, after 20 years you have about R1 089 129.
You put in about R406 791, so about R682 337 is growth.
With 4.5% inflation, that's worth about R451 599 in today's rands.

Saving for a specific target instead? Use the savings goal calculator. To keep the growth tax-free, see the TFSA calculator.

Frequently asked questions

What return should I use?

Historically, SA cash and money market accounts have returned roughly inflation + 1–2%, balanced funds around inflation + 4%, and equities around inflation + 5–7% over long periods. Past returns don't guarantee future returns.

Is interest on savings taxed in South Africa?

Interest is tax-free up to R23 800 a year (R34 500 if you're 65 or older). Above that, it's taxed at your marginal rate, unless you use a tax-free savings account.

How long does it take to double my money?

A quick estimate is the rule of 72: divide 72 by your annual return. At 10% a year, money doubles in about 7.2 years; at 6%, about 12 years.