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The Rule of 72
Ancient mathematical shortcut · Unknown (2026)
Confidence: High
To estimate how many years it will take for an investment to double given a fixed annual rate of return, divide 72 by that rate.
Core Concepts
The Problem
Investors need a quick way to understand the effect of compounding without complex calculations.
The Claim
Dividing 72 by the annual interest rate gives the approximate number of years to double your money.
Key Evidence
- •Approximation derived from logarithmic properties, accurate for rates between 5-10%.
Practical Implication
A simple mental model helps people evaluate investment returns and make better financial decisions.
Nuance & Limits
The Rule of 72 works best for compound interest and moderate interest rates.
Source Material
Citation Density
Ubiquitous in financial education
Gaps
- ⚠ Not always explained alongside limitations of high interest rates.
Who's Talking About This
1 episode reference this idea.
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