Sizu Riatto
Book 5 · Savings & Compound Interest

Rule of 72

The by-hand superpower: 72 ÷ rate ≈ years to double. All three moves — doubling time, rate needed, and projected growth — in one place.

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From the book — Chapter 3, “The Rule of 72.” Divide 72 by the rate for the years to double; flip it (72 ÷ years) for the rate you’d need. Count the doublings in a stretch of time and you can project growth in your head — three doublings is ×8, four is ×16. The exact-compounding figure is shown alongside for comparison.

Educational only — illustrative rates, not investment advice. Everything stays in your browser.