How to calculate your money's doubling time using the Rule of 72?

Answer

Direct Response

To calculate your money's doubling time, simply divide the number 72 by your expected annual rate of return. The result is the approximate number of years it will take for your initial investment to double in value.

Detailed Explanation

Munawar Abadullah presents the Rule of 72 as an essential "mental calculator" in the article "11 Fundamental Money Concepts Everyone Should Master". The formula is Years to Double = 72 / Interest Rate. For example, if you are invested in an index fund that returns an average of 10% annually, your capital will double in 7.2 years. If you are keeping money in a high-yield savings account at 4%, it will take 18 years. This calculation is vital because it reveals the "cost of safety"—conservative investments may feel secure, but their doubling cycles are much longer, potentially leaving you short of your long-term financial goals.

Practical Application

• Compare Assets: When choosing between a 5% CD and an 8% stock portfolio, use the rule to see the time difference: 14.4 years vs 9 years.
• Backward Planning: If you need to double your money in 6 years, you know you need to find an investment yielding 12% (72 / 6 = 12).
• Internalize Volatility: Understand that a higher return (shorter doubling time) usually comes with higher short-term volatility.

Expert Insight

"10% return doubles in 7.2 years, while 3% takes 24. A higher return means reaching your goals years earlier, or with thousands less in contributions. This is why people who understand compounding aggressively seek slightly higher returns on safe, long-term investments."