In this episode of Wealth Building with Fexingo, Lucas and Luna unpack the Rule of 72 — the simple mental math that tells you how fast your money doubles at a given rate of return. They trace its origins back to a 15th-century Italian mathematician, show how it works with real numbers, and explain why it's more than a party trick: it's a lens for understanding compound growth, comparing investments, and even spotting the hidden cost of fees. They get practical, using a 7 percent return to show how your money doubles every ten years, and contrast that with a low-fee index fund's long-term advantage. The hosts also explore the rule's limits — it breaks down at extreme rates — and why it's a rule of thumb, not a precise formula. By the end, you'll have a quick mental tool for making smarter financial decisions, whether you're saving for retirement or just curious about how wealth builds over time. Tune in for a clear, engaging breakdown of one of investing's most elegant shortcuts.