The precise version of this formula is 69.3 ÷ rate, derived from the natural logarithm of 2. 72 is used instead because it divides evenly by 1, 2, 3, 4, 6, 8, 9, and 12, making it easy to compute in your head at the cost of a small amount of accuracy.

🇵🇹 Works the same whether the return comes from a PPR, an ETF portfolio, or Certificados de Aforro, since it's a property of compounding itself, not of any particular product.