Nine years at 8%
The "Rule of 72" gives a good approximation of 72/4=18%.
Use the "rule of 72"...simply put, using compound interest you take the number 72 and divide it by the interest rate. Thus, at 5% the time to double is 14.4 years. This formula can be used for calculating a "double" for any interest rate using the same mathematical procedure.
The same time that it will take for any other amount to double. However, for the actual calculations you need to know the interest rate.
It is approx 65.52
If you have an annual interest rate then is 10.405%
A simple interest rate of 10 per cent per year will double a sum of money in ten years.
The rule of 72 is a quick and very accurate method of determining how long it takes for money to double at a specified rate of interest, compounded annually. For example, using the rule of 72 with a compounded interest rate of 6% it would take 12 years to double your money (72 divided by 6). The precise amount of time it takes to double your money at 6% based on the actual computation of compounded interest is 11.9 years. The rule of 72 works very well unless the rate of interest exceeds 20% at which point the error rate starts to deviate substantially from the actual answer. The rule of 72 can also be used to figure out what rate of interest you need to double your money in a specified number of years. For example, if you want to double your money in 5 years, divide 72 by 5 and the interest rate needed is 14.4%.
It will take 18 years.
If the interest rate was eight percent, it would take about 9 years to double your principle.
About 11 years. (One quick way to find out how fast your money will double is through the Rule of 72. Divide 72 by the interest rate you're getting--in this instance, 6.5%. 72 divided by 6.5 = 11.07. So, it will take a little over 11 years for your money to double.)
determining how many years it takes for money to double at a particular interest rate
20 YEARS
It is called the rule of 72. You take the interest rate you will be receiving and divide that number into 72. the answer will be the number of years it will take you to double your money at that interest rate.
About 8 years to double (divide 70 by the interest rate), and presumably another 8 years to double again? This supposes compound interest. For simple interest, 11 years to double and 33 to quadruple.
10 years. Compound interest would take 7 years.
Nine years at 8%