The $10/Day Millionaire
Compound interest and the Rule of 72
A 25-year-old who sets aside ten dollars a day in a low-cost index fund retires at 65 with roughly two million dollars. The same person, doing the same thing, starting at 35 instead of 25, retires with roughly seven hundred thousand. The cost of that ten-year delay is more than every dollar the late starter ever saves.
Compounding is unforgiving to procrastinators and lavishly generous to anyone who shows up early. Most beginners assume investing is about picking which stock will go up next. It isn't.
The single most consequential investing skill — the one that decides whether you retire wealthy or working — is letting time do its work on a small, steady amount of capital. The mechanism behind it has a sober name and an unsexy reputation: compound interest. Get it working for you and the math is so generous it looks unfair.
That is the opening. Finishing a lesson is where it stops being interesting and starts being useful: the full lesson runs to 9 sections and ends with 6 practice questions. A free account is what opens the rest, and the other 255 lessons in the Academy with it. No card.
What this lesson covers
- 1Compound interest, in plain language
- 2The three levers — and which one matters most
- 3The cost of waiting — ten years changes everything
- 4Compound Interest Calculator
- 5The compound growth formula
- 6What $10,000 becomes at different return rates
- 7Berkshire Hathaway, 1965 to 2023 — what compounding looks like in the real world
- 8Where to see this on the platform
- 9Summary