Rule of 72
The Rule of 72 is a mental shortcut for compound growth: divide 72 by your annual rate of return to estimate how many years it takes money to double. At 7% a year, money doubles in roughly 72 ÷ 7 ≈ 10 years; at 9%, about 8 years.
It works in reverse too — 72 divided by the years you have tells you the rate you'd need. The rule is an approximation that's most accurate for rates between about 5% and 12%, but it's remarkably handy for sanity-checking any growth or inflation figure in your head.
Put it to work
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