Exploration · Compound interest

The Doubler.

At 7.0%, your money doubles every 10.3 years (Rule of 72). Each bar below is one doubling — the last one is bigger than everything before it combined.

Starting amount
Horizon
Annual return7.0%
Each row is one doubling
  • start
    $10k
  • year 10
    $20k
  • year 21
    $40k
  • year 31
    $80k
  • year 41
    $160k
The last doubling alone

Added $80k. That’s 50% of your final $160k.

Every previous doubling combined produced the other half. The final 10-year window outweighed everything that came before.

Rule of 72 (72 / rate% ≈ years to double) is an approximation; exact doubling time is ln(2) / ln(1 + rate). Accurate to within a fraction of a year at 4–10% rates.
The Doubler — Explorations — Edmonds Instructor Hub