Concept · Numerical Business Rules
Rule of 72
Origin: Unknown origin, ancient/Renaissance banking
Biological Parallel
Bacterial cells divide with mathematical precision: E. coli doubles every 20 minutes under ideal conditions, making the Rule of 72 a literal description of exponential growth's clockwork. This doubling pattern is biology's default mode—from cancer cells to algal blooms—until carrying capacity intervenes. The rule works because natural logarithms govern both compound interest and cell division kinetics, revealing that bacterial growth and portfolio growth follow identical mathematical laws.