Return on investment (ROI) is a percentage that represents the net profit or loss (i.e., earnings) on an investment over a certain period of time.

　　In order to calculate ROI, you must first find the net profit or loss. Take the current or final value of your investment—including all the interest, dividends, and capital appreciation earned over time (but not any fees, commissions, or taxes)—and subtract the initial amount you invested. Take the resulting net value and divide it by the initial cost of your investment, then multiply by 100. The result is ROI expressed as a percentage, which is helpful for comparing two investments that are denominated in different currencies.

　　For example, suppose you paid $50 for 100 shares a stock (total cost of $5,000) and then sold them a year later for $55 per share (total proceeds of $5,500). Your net profit would be $500, which is the initial cost of the investment ($5,000) subtracted from its current value ($5,500). To find the ROI, you would divide your net profit by the initial investment ($5,000) and multiply the result (0.1) by 100, giving you a return on investment of 10%.

　　For an investment in the equities market, you might compare your return versus a benchmark, such as the S&P 500 or other stock index.

　　ROI is a helpful indicator of the general effectiveness of an investment, but it’s not comprehensive. It does not account for any capital gains tax or fees associated with the investment. Basic ROI also fails to account for compounding returns.

　　Although ROI can be calculated over any time period, it’s frequently expressed as an annual rate. Calculating annualized ROI is a bit more complicated. It can be determined using the following formula:

　　where ROI is expressed as a decimal and n is the number of years that the investment is held.

　　For example, suppose you own a stock for five years and it has an overall ROI of 60%, or 0.60. The annualized ROI would be [(1 + 0.60)^(1/5) – 1] x 100 = 9.86%.

　　Annualized ROI is more useful than simple ROI for comparing the profitability of different investments over different periods of time. For example, annualized ROI can help you determine whether a stock with an ROI of 40% over four years is more profitable than a stock with an ROI of 30% over three years.

　　ROI is a generally helpful tool, although it does not account for the risk or volatility of an investment. When you’re analyzing potential investments, ROI should be part of your due diligence, but not the only factor to consider.

　　Timothy Lake