Whether you want to evaluate offers that promise to "double your money fast" or establish investment goals for your portfolio, a quick-and-dirty method will show you how long it will take to double your money. It's called the Rule of 72 and can be applied to any investment.
How the Rule Works
To use the Rule of 72, divide the number 72 by an investment's expected annual return. The result is the number of years it will take, roughly, to double your money. For example, if the expected annual return of a bank Certificate of Deposit (CD) is 2.35% and you have $1,000 to invest, it will take 72/2.35 or 30.64 years for you to double your original investment to $2,000. If the expected annual return on a CD is 5% and you invest the same amount, it will take you 14.4 years to double your money.
CDs are great for safety and liquidity, but let's look at stocks. It's impossible to know in advance what will happen to stock prices. We know that past performance does not guarantee future returns. But by examining historical data, we can make an educated guess. According to Standard and Poor's, the average annualized return of the S&P index, which later became the S&P 500, from 1926 to 2020 was 10%. At 10%, you could double your initial investment every seven years (72 divided by 10). In a less-risky investment such as bonds, which have averaged a return of about 5% to 6% over the same period, you could expect to double your money in about 12 years (72 divided by 6).
Keep in mind that we're talking about annualized returns or long-term averages. In any given year, stocks might return 25% or lose 30%. Over a long period, the returns will average out to 10%. The Rule of 72 doesn't mean that you'll be able to take your money out of the stock market in 10 years. You might have doubled your money by then, but the market could be down, and you might have to leave your money in for several more years until things turn around. If you must achieve a certain goal or be able to withdraw your money by a certain time, the Rule of 72 isn't enough. You'll have to plan carefully, choose your investments wisely, and keep an eye on your portfolio.
Achieving Your Investment Goals
A professional financial advisor may be your best bet for achieving specific investing goals, but the Rule of 72 can help you get started. If you know that you need to have a certain amount of money by a certain date, for example, for retirement or to pay for your newborn child's college tuition, the Rule of 72 can give you a general idea of which asset classes you'll need to invest in to achieve your goal.
First, you can use the Rule of 72 to determine how much college might cost in 18 years if tuition increases by an average of 4% per year. Divide 72 by 4% and you know that college costs are going to double every 18 years.
Right now you have $1,000 to invest and with an 18-year time horizon, you want to put it all in stocks. We saw in the previous section that investing in the S&P 500 has historically allowed investors to double their money about every six or seven years. Your initial $1,000 investment will grow to $2,000 by year 7, $4,000 by year 14, and $6,000 by year 18. Suddenly 18 years isn't as long a time horizon as you thought, perhaps leading you to rethink your investment strategy.
The Bottom Line
While the Rule of 72 is a good investment guideline, it only provides a framework. If you're looking for a more precise outcome, you'll need to better understand an asset's future value formula. The Rule of 72 also does not take into account the effect of investment fees, such as management fees and trading commissions, can have on your returns. Nor does it account for the losses you'll incur from any taxes you have to pay on your investment gains.
FAQs
All you do is divide 72 by the fixed rate of return to get the number of years it will take for your initial investment to double. You would need to earn 10% per year to double your money in a little over seven years.
How to double your money every 7 years? ›
1 At 10%, you could double your initial investment every seven years (72 divided by 10). In a less-risky investment such as bonds, which have averaged a return of about 5% to 6% over the same period, you could expect to double your money in about 12 years (72 divided by 6).
What is the 7 year rule for doubling money? ›
The most basic example of the Rule of 72 is one we can do without a calculator: Given a 10% annual rate of return, how long will it take for your money to double? Take 72 and divide it by 10 and you get 7.2. This means, at a 10% fixed annual rate of return, your money doubles every 7 years.
What is the 7 year rule for compound interest? ›
For example, the Rule of 72 states that $1 invested at an annual fixed interest rate of 10% would take 7.2 years ((72 ÷ 10) = 7.2) to grow to $2. In reality, a 10% investment will take 7.3 years to double (1.107.3 = 2). The Rule of 72 is reasonably accurate for low rates of return.
What is the doubling money trick? ›
The Rule of 72 is a well-known shortcut for calculating how long it will take for an investment to double if its growth compounds annually. Just divide 72 by your expected annual rate of return. The result is the number of years it will take you to double your money.
What is the rule of 42? ›
One of the key rules within my unique Income Method is the Rule of 42 - holding at least 42 income-generating investments that enable you to have reduced risk from any individual holding.
What is the 7 rule in stocks? ›
The rule states that a company's stock price should either be seven times its earnings before interest, taxes, depreciation, and amortization (EBITDA) or 10 times its operating earnings per share. To apply the 7/10 rule, first determine the company's operating earnings per share or EBITDA.
How is the 7 year rule calculated? ›
The starting point is the so called "7-year rule" which says that the person making the gift must survive for 7 years from the date of the gift, for the value of the gift to fall out of their estate for IHT purposes.
Does a 401k double every 7 years? ›
One of those tools is known as the Rule 72. For example, let's say you have saved $50,000 and your 401(k) holdings historically has a rate of return of 8%. 72 divided by 8 equals 9 years until your investment is estimated to double to $100,000.
What is Rule 72 in savings? ›
It's an easy way to calculate just how long it's going to take for your money to double. Just take the number 72 and divide it by the interest rate you hope to earn. That number gives you the approximate number of years it will take for your investment to double.
To find out how many years it will take your investment to double, you can take 72 divided by your annual interest rate. For instance, if your savings account has an annual interest rate of 5%, you can divide 72 by 5 and assume it'll take roughly 14.4 years to double your investment.
Does the S&P 500 double every 7 years? ›
According to his math, since 1949 S&P 500 investments have doubled ten times, or an average of about seven years each time.
How do you calculate simple interest for 7 years? ›
How do you find the future value of simple interest?
- Write down the simple interest value, r , as a decimal (e.g., 5% is 0.05).
- Write down the present value, P .
- Set how many years in the future, t , you wish to calculate the future value for.
- Replace the parameters in the future value formula F = P × (1 + r × t) .
There are two approaches you could take. The first is increasing the amount you invest monthly. Bumping up your monthly contributions to $200 would put you over the $1 million mark. The other option would be to try to exceed a 7% annual return with your investments.
What is the magic number to double your money? ›
The Basics
To figure out how long it will take to double your money, take the fixed annual interest rate and divide that number into 72. Let's say your interest rate is 8%. 72 ∕ 8 = 9, so it will take about 9 years to double your money.
How do I double my money fast? ›
Trading options is one of the fastest ways to double your money – or lose it all. Options can be lucrative but also quite risky. But to double your money with them, you'll need to take some risk. The biggest upsides (and downsides) in options occur when you buy either call options or put options.
Is 7% annual return realistic? ›
In short, the average stock market return since the S&P 500's inception in 1926 through 2018 is approximately 10-11%. When adjusted for inflation, it's closer to about 7%.
How many years does a sum of money doubles itself in 7 years? ›
CONCEPT: Simple interest concept. Now, we want the money to be quadruple i.e. 4 times. ∴ The money will quadruple itself in 21 years.
