Compound interest is the most powerful force in the financial universe. It is interest earned on your interest. Over short periods, it smells like nothing. Over long periods, it looks like a miracle.
Defining Compound Interest
Simple interest is when you earn interest only on your original principal. Compound interest is when that interest is added back to your balance, so next time, you earn interest on a larger amount.
Pro Tip: The Rule of 72
Divide 72 by your interest rate to see how many years it takes for your money to double. (e.g., $72 / 10\% = 7.2$ years).
How the Math Works
If you invest $\$1,000$ at a $10\%$ annual return:
- Year 1: You earn $\$100$. Your balance is $\$1,100$.
- Year 2: You earn $10\%$ of $\$1,100$ ($\$110$). Your balance is $\$1,210$.
- Year 10: Your balance is approximately $\$2,593$.
- Year 30: Your balance is approximately $\$17,449$.
Notice the "hockey stick" growth. The longer the timeline, the steeper the gain.
The Cost of Waiting
Waiting just 10 years to start can cost you hundreds of thousands of dollars.
An investor who starts at age 25 and puts in $\$500$ a month until age 35, then stops entirely, will often have more money at retirement than an investor who starts at 35 and never stops.
Time > Money
When it comes to wealth building, the amount of time you are in the market is significantly more important than the amount of money you put in.
Making the Snowball Roll
How do you maximize compound interest? There are only three knobs you can turn:
- Time: Start as early as possible.
- Rate: Invest in assets with higher growth potential (like stocks vs savings).
- Principal: Add more money consistently.
Start Today, Not Tomorrow
You don't need a lot of money to start. You just need to start. Open a brokerage account or a high-yield savings account today, put in what you can, and let time do what it does best.