LONDON -- It's always worth keeping an eye on the earnings forecasts for your favorite companies, especially if you use forward price-to-earnings ratios to gauge when to buy and sell your shares.

You never know, if City brokers have been revising their projections of late, your investments may not be as cheap -- or expensive -- as you think!

Today I'm looking at the earnings per share forecasts for GlaxoSmithKline (LSE:GSK) (NYSE:GSK), the FTSE 100 pharmaceutical company. All my figures are courtesy of S&P Capital IQ.

The consensus for 2012 is for earnings per share of 112 pence, which puts the 1,364 pence shares on a forward P/E ratio of 12.

The estimates also suggest earnings may rise to 119 pence per share for 2013 and increase further to 132 pence for 2014.

Earnings may then advance to 145 pence per share for 2015, then climb to 155 pence per share for 2016, at least according to City analysts.

The data from S&P Capital IQ also indicates GSK's revenues may only grow at around 3% a year from about 26.7 billion pounds in 2012 to 30.8 billion pounds in 2016.

All told, the forecasts aren't great, with revenues essentially predicted to go nowhere between 2012 and 2016. But then again, that P/E of 12 looks like the market is already expecting growth to be subdued.

Whether these projections make GlaxoSmithKline a buy, a hold, or a sell is, of course, up to you. To put the company's multiple into perspective, the FTSE 100 at 5,842 trades on a P/E of 11.4.

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David Kuo owns shares in GlaxoSmithKline. The Motley Fool has no positions in the stocks mentioned above. Motley Fool newsletter services recommend GlaxoSmithKline. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.