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The Rule of 72: How Fast Will Your Money Double?
A back-of-the-napkin trick that tells you in seconds how long it takes an investment to double — plus when it's accurate and three handy variations.
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Compound vs. Simple Interest: What's the Difference?
The formulas, a side-by-side example over 30 years, and where each type shows up in real life — from savings accounts to car loans and credit cards.
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Why Starting Early Beats Everything: The Time Value of Compounding
How a few extra years can outweigh thousands of extra dollars, the real cost of waiting, and what to do if you're getting a late start.
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