What Is Compound Interest? A Beginner's Guide to Wealth Building
Discover what compound interest is, how the math works, and why starting early is the most powerful way to build long-term wealth.
Key lesson
Compound interest is when you earn interest on both the money you saved and the interest it has already earned. Starting early is the most powerful way to make your money grow.
What is compound interest?
Albert Einstein reportedly called compound interest the eighth wonder of the world, adding that he who understands it earns it and he who does not pays it. Simply put, compound interest is the interest you earn on both your original money and on the interest you keep accumulating.
When you put money in a savings account or an investment, it earns a return. If you leave that return in the account, it gets added to your principal balance. The next time interest is calculated, it is based on that new, larger balance. Over time, this creates a snowball effect where your money grows faster and faster.
Simple interest vs. compound interest
Simple interest is calculated only on the principal amount you deposited. If you invest $1,000 at a 5% simple interest rate, you earn $50 every single year, regardless of how long you leave the money there.
Compound interest is calculated on the principal and the accumulated interest of previous periods. If you invest $1,000 at a 5% compound interest rate, you earn $50 in year one. In year two, you earn 5% on $1,050, which is $52.50. In year three, you earn 5% on $1,102.50, which is $55.13. Over decades, the difference becomes massive.
The Rule of 72
The Rule of 72 is a quick way to estimate how fast your money will double at a given annual rate of return. Simply divide 72 by your expected annual interest rate. For example, if you expect an 8% return, 72 divided by 8 equals 9. That means your money will double approximately every 9 years.
Why time is your best asset
When it comes to compound interest, time is far more important than the amount of money you start with. Because your money grows exponentially, the longest period of growth happens at the very end of your investment timeline. This is why starting to save and invest in your 20s gives you a massive advantage over someone who starts in their 30s or 40s.
How to make compound interest work for you
Here are the best ways to take advantage of compound interest:
- Start as early as possible, even with small amounts.
- Reinvest all your earnings, dividends, and interest.
- Contribute consistently by setting up automatic transfers.
- Leave the money alone to let it grow uninterrupted.