Here's How Long It Takes to Double Your Money

The quickest way to double your money is to fold it in half and put it in your back pocket. -- Attributed to Will Rogers and others

Will Rogers is rightfully considered a witty quipster, among other things, but he probably wouldn't have been a great financial advisor. It is good to have a solid grasp of how to double your money, though, as it can help you in your financial planning -- especially for retirement.

Here's a look at how money doubles -- and what kind of growth you might shoot for in your financial life.

Image source: Getty Images.

The Rule of 72

Let's start with the rather cool Rule of 72, which lets you do the doubling-your-money math in your head. The rule says that if you divide 72 by your growth rate, you'll get the number of years it will take to double your money -- and vice versa. Here's what the rule would suggest.

Calculations by author.

Calculations by author.

The rule runs into problems at the extremes. Imagine, for example, that your growth rate was 72%. The rule would suggest that you would double your money in just one year -- but you'd actually need a 100% growth rate in order to double in one year.

More precise numbers

Most of us will be dealing with numbers near the middle of the tables, where they're more accurate, but just for your edification, this table offers more precise doubling periods, based on logarithmic calculations:

Data source: visualcapitalist.com. Calculations by author.

Examples of how money can grow

Let's put these growth aids to work: Imagine, for example, that you sock $25,000 into an investment that grows by about 5% annually. In 14.2 years, it will have doubled to $50,000. In another 14.2 years, it will reach $100,000.

Of course, most of us would like to double our money more briskly than that, and that's a reasonable goal -- after all, the long-term average annual return of the stock market is around 10%. Here's how your money would grow if you started with $25,000 when you were 35, doubling every 7.3 years:

Calculations by author.

Clearly, a sizable nest egg can be amassed by investing in the stock market. Keep in mind, though: While some returns can be guaranteed, or close to guaranteed, like government bonds and certificates of deposit (CDs), the stock market's gains are less predictable. Over your investing period you could average 8% or 12% or more or less than that.

Remember, too, that you're unlikely to just invest a lump sum once and let it grow until you retire. Instead, for best results, you'll want to keep investing more money over a long period, letting it compound over many years.

Effective investing

If you want to get close to the stock market's return over a long period, all you need to do is invest in one or more low-fee index funds, such as one that tracks the S&P 500 or a broader market index.

Here are some possibilities:

• SPDR S&P 500 ETF (SPY)
• Vanguard Total Stock Market ETF (VTI)
• Vanguard Total World Stock ETF (VT)

If your investments grow by 8% annually over a long period, here's what you might amass:

Calculations by author.

Put all this information together and act on it, and you might be doubling your money much more quickly than every seven or 14 years. Just don't procrastinate, because your earliest invested dollars are your most powerful ones.