What is Compound Interest?
Compound interest is often called the "eighth wonder of the world" — a quote commonly attributed to Albert Einstein (though there's no evidence he actually said it). Regardless of its origin, the sentiment captures how powerful compounding can be.
Unlike simple interest, which only earns returns on your original investment, compound interest earns returns on your returns. This creates an exponential growth curve that accelerates over time.
The Mathematics
The formula for compound interest is:
A = P(1 + r/n)^(nt)
Where:
- A = Final amount
- P = Principal (initial investment)
- r = Annual interest rate (decimal)
- n = Number of times interest compounds per year
- t = Time in years
A Real-World Example
Let's say you invest $10,000 at 7% annual return for 30 years:
- After 10 years: $19,672
- After 20 years: $38,697
- After 30 years: $76,123
Your money grew by more in the last 10 years ($37,426) than in the first 20 years combined ($28,697). This is compounding in action.
Key Takeaways
- Start early: Time is the most powerful factor in compound interest
- Be consistent: Regular contributions dramatically accelerate growth
- Stay invested: Pulling money out resets your compounding clock
- Reinvest dividends: Let your returns generate more returns
How Regular Contributions Help
If you add just $500 per month to that same $10,000 investment at 7%:
- After 30 years: $682,000+
The combination of regular contributions and compound interest creates wealth much faster than either alone.