72 Division Investment Rule

The 72 Rule is a quick mental math shortcut to estimate how long it takes for an investment to double based on its return rate.

Core Concept

• Divide 72 by the expected return rate to estimate years until investment doubles
• For example: 72 divided by 10% return = ~7 years to double
• Works for returns between 7-10% nominal rate
• Actual doubling time is approximately 7-10 years for typical market returns

Key Investment Principles Related to Rule

• Compound interest becomes powerful over longer time periods
• Regular contributions accelerate growth
  • Not just one-time investments
  • Described as "pushing a train that goes faster and faster"
• 7-8% average annual returns are actually phenomenal when compounded
  • Don't need aggressive or risky investments
  • Simple index funds can provide these returns

Practical Application

• Use for quick mental math estimates
• Don't need exact precision for planning
• Helps demonstrate power of compound interest
• Shows why starting early matters
• Validates "boring" investment approaches that rely on time and consistency

Investment Philosophy

• Focus on average, consistent returns over time
• Don't chase aggressive returns
• Let compound interest do the work
• Keep contributing regularly
• Stay invested for the long term