Rule of 72

The Rule of 72 is mental math for compounding speed: 72 divided by the annual percentage return approximates the years for money to double. At 7.1% money doubles in about ten years; at 3% it takes about twenty-four. It also works on the leaks — at 4% inflation, idle cash loses half its buying power in about eighteen years.

First used in: 0.2 · Your money as a system