Compound interest means you earn interest on your original amount and on the interest you have already earned. Over long periods, that second layer does most of the work. It is the reason regular saving starts paying off faster than most people expect.
Simple interest vs compound interest
With simple interest, you earn the same amount each year on your original deposit. With compound interest, the interest is added to the balance, and the next year’s interest is calculated on the larger total.
A worked example
Suppose you deposit 10,000 at an annual return of 8%, and leave it untouched for 10 years:
- With simple interest, you earn 800 each year, for a total of 18,000.
- With annual compounding, the balance grows to about 21,590.
The gap is about 3,590 from the same starting amount. The longer the money stays invested, the bigger the gap becomes.
The rule of 72
To estimate how long money takes to double, divide 72 by the annual rate. At 6%, money roughly doubles in 12 years. At 9%, it takes about 8 years. This is an estimate, not an exact figure, but it is useful for comparing options quickly.
Why time matters more than the amount
Starting early often beats saving more later. Someone who invests a smaller sum from age 25 can end up with more than someone who starts at 35 with a larger sum, because the early money has more years to compound.
Where compounding works against you
Compound interest also applies to debt. Unpaid credit card balances can grow quickly, and missed payments can add fees and interest on top. Paying off high-interest debt is often the best guaranteed return available to you.
How to put compound interest to work
- Start with an amount you can keep up for years, even if it is small.
- Automate a fixed monthly contribution so the habit continues in quiet months.
- Reinvest interest and dividends rather than spending them.
- Keep fees low, because they reduce the amount that compounds.
- Review your plan once a year, not every week.
Frequently asked questions
Does compound interest work on savings accounts?
Many savings and deposit products compound interest, often monthly or quarterly. Check the terms for how often interest is added and whether the rate is fixed or variable.
Is a higher return always better?
Not on its own. Higher expected returns usually come with more risk, and returns are not guaranteed. Compare returns after fees and consider how much risk you can tolerate.
What is the best time to start?
Now is usually better than later, because each year of delay means losing a year of compounding. Start with what you can afford and increase it over time.
This guide is for general information only. Returns are not guaranteed. For advice on your own situation, speak to a qualified financial adviser.
