Simple but yet powerful. A rule that provide the estimated time to reach your goal.
If an investment provide a regular return of 10% per annum and you reinvested that return, it will take 7.2 years to double your initial investment.
How? 72 divided 10% p.a. = 7.2 years
There are bank and shares paying dividends like 15 - 20 % p.a. Find them and put your money there...practically every ~ 5 years you double your initial investment!
Alternatively, reversing the equation give the rate of investment return required for specified number of years to double the initial investment.
How? 72 divided 5 years = 14.4%
Chance favour the prepared mind -- Louis Pasteur