What is Einstein’s Rule of 72?

The rule of 72 is a rule of thumb (credited to Albert Einstein) that investors use to approximate the time it takes for money to double at a given rate of return. It states that if you divide the number 72 by any given rate of return, the answer you get is the time it takes for money to double at that given interest rate (assuming you can get the same rate each year and it is compounded annually). For example, if you earn 10% on your money it would double in 7.2 years (72 divided by 10 = 7.2). The value 72 is a convenient choice of numerator, since it has many small divisors: 1, 2, 3, 4, 6, 8, 9, and 12. It provides a good approximation for annual compounding, and for compounding at typical rates (from 6% to 10%). The approximations are less accurate at higher interest rates.