Compounding
Small gains that build on themselves grow slowly, then astonishingly fast.
Also known as: Compound interest, The eighth wonder
beginner Mathematics of exponential growth
Compounding is growth that feeds on its own results: each period's gain becomes part of the base that grows next period. Because the effect is exponential, it looks unimpressive for a long time and then accelerates dramatically.
What it is
With simple growth, you add the same amount each period. With compounding, you add a percentage of an ever-larger base, so the increments themselves grow. Money left to compound, skills that make learning the next thing easier, relationships that deepen with each interaction — all follow the same curve.
The counterintuitive part is the shape. For most of the timeline the line looks nearly flat, which is why people quit early: the payoff is back-loaded. The dramatic returns arrive late, and they depend entirely on not interrupting the process. Consistency and time matter more than the size of any single gain.
Compounding also runs in reverse. Debt, neglected maintenance, and small daily bad habits compound into large problems by exactly the same mechanism.
Worked example
Save £200 a month at a 7% annual return. After 10 years you have roughly £34,000 — not life-changing. Keep going untouched: after 30 years it's around £240,000, and the last decade alone adds more than the first two combined. Nothing changed except time, yet the final stretch dwarfs the beginning. That back-loaded curve is compounding.
Failure mode — when it misleads
Assuming compounding is guaranteed or smooth is the trap — returns are volatile, growth rates change, and interrupting the process (withdrawing, quitting, breaking the streak) resets the base. It also can't run forever in a finite world; real curves eventually hit limits. Compounding rewards patience, but blind faith in an extrapolated curve is its own error.
How to apply it
- Start early — time in the process matters more than the size of each step.
- Protect the base: avoid interruptions and withdrawals that reset the curve.
- Watch for negative compounding in debts and neglected habits.
- Don't judge a compounding effort by its flat early years.
Related entries
Sources & further reading
The Psychology of Money
by Morgan Housel · book
Housel argues that compounding, and the patience it demands, explains most long-run financial outcomes.
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