what is the difference between the rule of 72 and the rule of 73 
the rule of 72 primarily works with interest rates or rates of return that fall in the range of 6 and 10 when dealing with rates outside this range the rule can be adjusted by adding or subtracting 1 from 72 for every 3 points the interest rate diverges from the 8 threshold for example the rate of 11 annual compounding interest is 3 percentage points higher than 8 hence adding 1 for the 3 points higher than 8 to 72 leads to using the rule of 73 for higher precision for a 14 rate of return it would be the rule of 74 adding 2 for 6 percentage points higher and for a 5 rate of return it will mean reducing 1 for 3 percentage points lower to lead to the rule of 71 for example say you have a very attractive investment offering a 22 rate of return the basic rule of 72 says the initial investment will double in 3 27 years however since 22 8 is 14 and 14 3 is 4 67 5 the adjusted rule should use 72 5 77 for the numerator this gives a value of 3 5 years indicating that you ll have to wait an additional quarter to double your money compared to the result of 3 27 years obtained from the basic rule of 72 the period given by the logarithmic equation is 3 49 so the result obtained from the adjusted rule is more accurate for daily or continuous compounding using 69 3 in the numerator gives a more accurate result some people adjust this to 69 or 70 for the sake of easy calculations 