As investors, we need to understand how our companies truly make their money. A neat trick developed for just that purpose -- the DuPont formula -- can help us do so.

The DuPont formula can give you a better grasp on exactly where your company is producing its profit, and where it might have a competitive advantage. Named after the company where it was pioneered, the formula breaks down return on equity into three components:

Return on equity = net margin x asset turnover x leverage ratio

What makes each of these components important?

  • High net margins show that a company can get customers to pay more for its products. Luxury-goods companies provide a great example here.
  • High asset turnover indicates that a company needs to invest less of its capital, since it uses its assets more efficiently to generate sales. Service industries, for instance, often lack big capital investments.
  • Finally, the leverage ratio shows how much the company is relying on liabilities to create its profits.

Generally, the higher these numbers, the better. That said, too much debt can sink a company, so beware of companies with very high leverage ratios.

Let's see what the DuPont formula can tell us about Ameren (NYSE: AEE) and a few of its sector and industry peers:

Company

Return on Equity

Net Margin

Asset Turnover

Leverage Ratio

Ameren

1.9%

1.9%

0.32

2.96

CenterPoint Energy (NYSE: CNP)

15.1%

5.0%

0.44

6.83

Exelon (NYSE: EXC)

19.6%

13.7%

0.37

3.87

PPL (NYSE: PPL)

13.7%

11.0%

0.31

3.85

Source: Capital IQ, a division of Standard & Poor's.

A quick scan down the right-most column and you can see how utilities make their money: operating leverage. With asset turnover in a fairly narrow range, the key differentiator comes down to margin. Ameren's net margin checks in at just 1.9%, well below those of rivals. CenterPoint juices its relatively lower net margin with the highest leverage of this bunch, while Exelon and PPL are able to put up much higher margin figures, leading to ROE in the teens.

Using the DuPont formula can often give you some insight into how a company is competing against peers and what type of strategy it's using to juice return on equity. To find more successful investments, dig deeper than the earnings headlines. If you'd like to add these companies to your watchlist, or set up a new one, just click here .

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Jim Royal, Ph.D., owns shares of Exelon. Exelon is a Motley Fool Inside Value pick. Motley Fool Options has recommended a covered strangle position on Exelon. Try any of our Foolish newsletter services free for 30 days. The Motley Fool has a disclosure policy.