As a rough guide to double any amount compounded annually, divide 70 by the interest rate. In this case that is 14 years.
Nine years at 8%
There is what's called the "rule of 72" which states, you divide the percent into 72 and that tells you how log it takes to double your money. For example, 4.6 goes into 72 15.65 times. So, it would take 15.65 years to double your money. That's not too good of an investment. 72 ÷ 4.6 = 15.65
8 years.
It will take 20 years.
11 years
12 years.
12 years
It will take 18 years.
About 13 years at 5.5%
17 years
Prices will double in approximately 24 years with a three percent rate of inflation.
If the interest rate was eight percent, it would take about 9 years to double your principle.
To double takes, don't ask me why, 70/x years where x is the interest rate, so 14 years give or take a month or two.
Nine years at 8%
Six years at 12%
Twelve years at 6%
Nine years at 8%