Doubling your investment is a great goal. But how long will it take?

The "Rule of 72" can help you estimate this quickly without spreadsheets.
Simply divide 72 by your investment's rate of return, and you'll get the approximate number of years it takes for your money to double — say, from 100k to 200k.

For example, with a 12% return, your investment will double in about 72/12 = 6 years. With a 10% return — 72/10 = 7.2 years.

The formula can also be "flipped" to estimate what rate of return you'd need to double your money within a chosen timeframe.
For instance, to double your money in 2 years, you'd need a return of roughly 72/2 = 36%. Over 5 years, it's about 72/5 = 14.4%.

The Rule of 72 is based on a rough approximation of the compound interest formula. It's not perfectly precise compared to the actual formula, but for a quick mental estimate — it's exactly what you need.