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Before making any investment decision, one of the key elements you face is working out the real rate of return on your investment.

Compound interest is critical to investment growth. Whether your financial portfolio consists solely of a deposit account at your local bank or a series of highly leveraged investments, your rate of return is dramatically improved by the compounding factor.

With simple interest, interest is paid just on the principal. With compound interest, the return that you receive on your initial investment is automatically reinvested. In other words, you receive interest on the interest.

But just how quickly does your money grow? The easiest way to work that out is by using what’s known as the “Rule of 72.” Quite simply, the “Rule of 72” enables you to determine how long it will take for the money you’ve invested on a compound interest basis to double. You divide 72 by the interest rate to get the answer.

For example, if you invest $10,000 at 10 percent compound interest, then the “Rule of 72” states that in 7.2 years you will have $20,000. You divide 72 by 10 to get the time it takes for your money to double. The “Rule of 72” is a rule of thumb that gives approximate results. It is most accurate for hypothetical rates between five and 20 percent.

While compound interest is a great ally to an investor, inflation is one of the greatest enemies. The “Rule of 72” can also tell you how long it will take for inflation to cut the buying power of your money in half.

Let’s say you decide not to invest your $10,000 but hide it under your mattress instead. Assuming an inflation rate of 4.5 percent, 72 divided by 4.5, in 16 years your $10,000 will have lost half of its value.

The real rate of return is the key to how quickly the value of your investment will grow. If you are receiving 10 percent interest on an investment but inflation is running at 4 percent, then your real rate of return is six percent. In such a scenario, it will take your money 12 years to double in value.

The “Rule of 72” is a quick and easy way to determine the value of compound interest over time. By taking the real rate of return into consideration (nominal interest less inflation), you can see how soon a particular investment will double the value of your money.

The “Rule of 72” is a mathematical concept, and the hypothetical return illustrated is not representative of a specific investment. Also note that the principal and yield of securities will fluctuate with changes in market conditions so that the shares, when sold, may be worth more or less than their original cost. The “Rule of 72” does not include adjustments for income or taxation. It assumes that interest is compounded annually. Actual results will vary.

How Can I Better Manage My Short-Term Cash?

The most important attribute of a cash reserve is its availability in time of sudden need. And even though a federally insured savings account is considered one of the safest places to put money being reserved for emergencies you may want to consider other alternatives when interest rates are low.

When selecting ways to invest your cash reserve, you should balance your liquidity needs with potential returns. Short-term investment instruments, such as Treasury bills, certificates of deposit, and money market mutual funds, can provide you with the liquidity needed to meet expected and unexpected expenses and to increase your short-term investment income.

By actively managing your short-term reserves, you can provide a means of saving for the future. You can use this money to increase your net worth with little or no additional risk to your principal. It’s important to remember that because income and personal circumstances are subject to change, you should conduct a periodic review of your cash reserve and its structure.

Note: Treasury bills are backed by the full faith and credit of the U.S. government as to the timely payment of principal and interest.

Note: Bank CDs are insured by the FDIC for up to $250,000 per depositor, per federally insured institution.

Money market funds are neither insured nor guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although money market funds seek to preserve the value of your investment at $1 per share, it is possible to lose money by investing in a money market fund.

Mutual funds are sold by prospectus. Please consider the investment objectives, risks, charges, and expenses carefully before investing. The prospectus, which contains this and other information about the investment company, can be obtained from your financial professional. Be sure to read the prospectus carefully before deciding whether to invest.

MANA welcomes your comments on this article. Write to us at [email protected].