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Glossary

Compound interest

Returns that themselves earn returns, so growth accelerates over time.

Simple interest pays you on your original amount. Compound interest pays you on your original amount plus every gain it has already made. Over one year the difference is trivial. Over thirty it is the difference between doubling your money and multiplying it by ten.

Compounding is why time in the market matters more than timing it, and why the boring advice to start early is genuinely the highest-leverage financial decision most people ever make. It is also why high-interest debt is so destructive - the same mechanism, running against you.

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