I started investing at 28. It wasn’t until two years after becoming a teacher that I’d built up an emergency fund and bought my first index ETF. When I calculated it later, I realized that if I had started at 25, I could have had roughly 40% more wealth by age 60 with the exact same monthly investment. A 3-year difference creates a 40% difference. That is the power of compound interest.
What Is Compound Interest?
Compound interest is a structure where interest accrues on the principal, and then interest accrues on that interest. The compound interest formula: FV = PV × (1 + r)^n
Related: index fund investing guide
Example: Investing 1,000,000 KRW at an annual return of 10%
In my experience, the biggest mistake people make is
Last updated: 2026-04-03
Your Next Steps
- Today: Pick one idea from this article and try it before bed tonight.
- This week: Track your results for 5 days — even a simple notes app works.
- Next 30 days: Review what worked, drop what didn’t, and build your personal system.
Disclaimer: This article is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions about a medical condition.
About the Author
Written by the Rational Growth editorial team. Our health and psychology content is informed by peer-reviewed research, clinical guidelines, and real-world experience. We follow strict editorial standards and cite primary sources throughout.
References
- [1] Federal Reserve Bank of St. Louis. (2023). Consumer Price Index. FRED Economic Data.
- [2] Siegel, J. J. (2014). Stocks for the Long Run (5th ed.). McGraw-Hill.
- [3] Bogle, J. C. (2007). The Little Book of Common Sense Investing. Wiley.
- [4] Malkiel, B. G. (2019). A Random Walk Down Wall Street. W. W. Norton.
- [5] Vanguard Group. (2022). The power of compounding. Vanguard Research.
Sound familiar?
Key Takeaways and Action Steps
Use these practical steps to apply what you have learned about Compound:
- Start small: Pick one strategy from this guide and start it this week. Consistency matters more than perfection.
- Track your progress: Keep a simple log or journal to measure changes related to Compound over time.
- Review and adjust: After two weeks, evaluate what is working. Drop what is not and double down on effective habits.
- Share and teach: Explaining what you have learned about Compound to someone else deepens your own understanding.
- Stay curious: This field evolves. Revisit updated research on Compound every few months to refine your approach.
