Tomorrow is earnings day for two-time Motley Fool Stock Advisor recommendation American Healthways (NASDAQ:AMHC). In case you haven't heard, the company reports its fiscal Q1 2006 earnings after market close.

Of course, if you haven't heard of American Healthways, that's entirely understandable. It's not exactly a household name, partly because its business doesn't make for the most pleasant of conversations -- unless you happen to enjoy discussing hepatitis C, coronary artery disease, end-stage renal disease, incontinence, or similarly happy subjects.

Unpleasant as these topics may be, helping to treat these diseases has proven to be a real moneymaker for both the company and its shareholders. In the eight months since Stock Advisor co-analyst Tom Gardner singled out American Healthways, its stock has returned 44% for our members, against less than 6% for the market at large.

That said, the company does appear to be slowing down on the earnings front. Last fiscal year (2005), it grew earnings by 24% over fiscal 2004. The year before that, earnings growth was 34%. And the year before that, 75%. Tomorrow, analysts are calling for growth to come in at a measly 5%.

That's the basic story, at least. American Healthways earned $0.22 per share in fiscal Q1 2005; it should earn $0.23 in fiscal Q1 2006; therefore, most people would argue that growth has stagnated. But that's oversimplifying the matter. For one thing, if all goes as analysts predict, the company won't even report earning the $0.23 in net profits. Rather, its net profits under GAAP would be closer to the $0.17 to $0.18 that the company itself promised three months ago.

How does this work? Well, start with the assumption that American Healthways' core operations earned $0.30 per share in fiscal Q1 2006 (which is what analysts believe happened). From that, subtract $0.01 for investments the company is making internationally, and another $0.06 for investments in its domestic Medicare Health Support (MHS) pilot programs. That gets you down to the $0.23 that constitutes the "consensus estimate" of American Healthways' pro forma earnings for the quarter. Now knock off another $0.06 for expensing stock options and other compensation, and you'll arrive at the company's own estimate for net earnings: $0.17.

Confusing? No doubt. There will be a whole host of variables at play when investors try to digest tomorrow's results. But as you try to figure out where the company's growth curve is headed, at least now you'll know what those variables are.

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Fool contributor Rich Smith holds no financial position in American Healthways.