As earnings season gets underway and investors start listening to calls and reading reports, understanding how companies report earnings is critical. Earnings per share. Basic EPS. Diluted EPS. Adjusted net income diluted. GAAP earnings. Non-GAAP earnings. Enough already.

Although confusion can be part of the learning process in investing, it is frustrating to spend time reading an earnings release and emerge foggy-headed. As a nascent analyst a few years ago, I was no different. Has the fog cleared? It's not any easier now, but I've gotten used to it and know what to look for. Below is a cheat sheet that I wish someone had given me when I started reading earnings reports.

Your prerequisite is a fundamental understanding of earnings per share (EPS), which is simply net income (earnings) divided by the number of shares outstanding. We'll focus here on the difference between GAAP earnings and adjusted, or non-GAAP earnings.

EPS figures come in two flavors. "Basic" uses the current number of common shares outstanding as the EPS denominator. "Diluted" EPS adds to the number of shares outstanding the potential dilution lurking in the form of convertible securities like options, warrants, and convertible debt -- and assumes they are converted to common stock. Diluted EPS is a more conservative metric since earnings are spread out over more shares. Absent a reference to diluted or basic EPS in a company release or the financial press, assume diluted share count, as that's the more commonly discussed figure.

GAAP earnings vs. adjusted earnings
Companies report their earnings according to GAAP, or Generally Accepted Accounting Principles, which is the common set of accounting principles all companies are expected to follow.

In order to get a cleaner picture of core operating earnings, some companies also report adjusted or non-GAAP earnings. They do this by adding back charges and subtracting gains. Non-recurring gains are subtracted from GAAP earnings, while non-recurring charges are added.

Those companies that report adjusted earnings will usually have a nice section of the earnings press release called something like "Reconciliation of GAAP net income (loss) to adjusted net income."

The good news is that we're getting closer to true operating earnings; the bad news is that all companies use different methods to get there. As a result, there's usually a disclaimer in the earnings report, something like, "adjusted net income per share does not have any standardized meaning prescribed by GAAP." As always, investors should exercise caution when taking the company's numbers at face value. More on that shortly.

Importantly, the "consensus analyst estimate" number is almost always based on some sort of core operating earnings since analysts typically build their financial models excluding extraordinary charges.

So what are these mysterious "adjustments"? In a nutshell, they are not part of the day-to-day operating expenses of a company and are therefore "adjusted," or either backed out of or added to GAAP earnings. To add to the confusion, adjustments and non-GAAP earnings are called by different names.

Different names for adjustments:

  • Non-recurring charges/gains
  • One-time items
  • Extraordinary items
  • Adjustments

Different names for non-GAAP earnings:

  • Pro forma earnings
  • As adjusted earnings

Examples of non-recurring charges are store closings, like the $30 million charge just reported by CircuitCity (NYSE:CC) in its fiscal fourth quarter, or Microsoft's (NASDAQ:MSFT) massive $714 million charge related to antitrust litigation for its third quarter (both charges would be added back to earnings). An example of a one-time gain is Circuit City's $1.8 million from the sale of a corporate office building (this is subtracted from earnings). These one-time EPS-affecting items are typically presented net of taxes.

Adjusting Research In Motion's fourth quarter
Research In Motion (NASDAQ:RIMM), maker of the BlackBerry, recently reported its fiscal fourth quarter ended Feb. 26, which shows just how much adjustments can matter. Research In Motion reported a GAAP net loss for the quarter of $2.6 million or -$0.01 per diluted share. Adjusted for extraordinary items, net income was $140.1 million or $0.71 per share. Wow! What happened?

Like Microsoft, Research In Motion was involved in some nasty litigation and concluded a patent infringement settlement with NTP, an Arlington, Va.-based patent holding company, taking a $294.2 million charge for the quarter. Partially related to the litigation, Research In Motion also recorded a $151.6 million tax asset gain. Neither were part of normal operations and both must be adjusted.

Here's how:

GAAP net loss $(2,573)

Litigation expense 294,194

Tax provision (151,556)

Adjusted net income $140,065

Research In Motion does a nice job of explaining its adjustments in its earnings release, including the non-GAAP reconciliation recreated above.

Beware recurring non-recurring charges
Beware of companies that use adjustments that occur too frequently. Simply put, non-recurring charges are expected to be, well, non-recurring. This was a favorite accounting trick during the Internet era, when companies pushed the envelope by classifying as extraordinary items charges that might more properly be considered operating expenses, thus overstating earnings.

When do charges occur too frequently? While there is no rule of thumb -- this is one of those accounting grey areas -- taking more than one of the same charge (or gain) and calling it non-recurring within any four quarters (the definition for current assets) might be sketchy. Any good analyst or investor needs to make that call, and include the charge in operations if justified.

Finally, some context: Earnings aren't the Holy Grail. There are plenty of other good metrics to use in evaluating a company, like structural free cash flow and return on invested capital. But understanding earnings reports and knowing how companies make adjustments is an essential part of any investor's tool kit.

Fool contributor ChrisCather owns none of the companies mentioned.