While some investors are already well versed in financial metrics (hat tip), this article is for those who would like to learn about Return On Equity (ROE) and why it is important. To keep the lesson grounded in practicality, we'll use ROE to better understand Marathon Petroleum Corporation (NYSE:MPC).

Marathon Petroleum has a ROE of 9.6%, based on the last twelve months. That means that for every $1 worth of shareholders' equity, it generated $0.10 in profit.

View our latest analysis for Marathon Petroleum

How Do I Calculate Return On Equity?

The formula for ROE is:

Return on Equity = Net Profit (from continuing operations) ÷ Shareholders' Equity

Or for Marathon Petroleum:

9.6% = US$4.2b ÷ US$44b (Based on the trailing twelve months to September 2019.)

Most readers would understand what net profit is, but it’s worth explaining the concept of shareholders’ equity. It is all earnings retained by the company, plus any capital paid in by shareholders. You can calculate shareholders' equity by subtracting the company's total liabilities from its total assets.

What Does Return On Equity Signify?

ROE looks at the amount a company earns relative to the money it has kept within the business. The 'return' is the profit over the last twelve months. That means that the higher the ROE, the more profitable the company is. So, as a general rule, a high ROE is a good thing. That means ROE can be used to compare two businesses.

Does Marathon Petroleum Have A Good Return On Equity?

One simple way to determine if a company has a good return on equity is to compare it to the average for its industry. The limitation of this approach is that some companies are quite different from others, even within the same industry classification. As is clear from the image below, Marathon Petroleum has a lower ROE than the average (12%) in the Oil and Gas industry.

That certainly isn't ideal. We prefer it when the ROE of a company is above the industry average, but it's not the be-all and end-all if it is lower. Nonetheless, it could be useful to double-check if insiders have sold shares recently.

How Does Debt Impact ROE?

Most companies need money -- from somewhere -- to grow their profits. The cash for investment can come from prior year profits (retained earnings), issuing new shares, or borrowing. In the case of the first and second options, the ROE will reflect this use of cash, for growth. In the latter case, the debt required for growth will boost returns, but will not impact the shareholders' equity. In this manner the use of debt will boost ROE, even though the core economics of the business stay the same.