Don’t get too excited about this earnings season by Nin-Hai Tseng @FortuneMagazine January 10, 2013, 3:48 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons FORTUNE – Earnings season may have had a strong start this week, but growth across corporate America’s bottom line during the busiest shopping months of the year is expected to slow. On Tuesday, Alcoa AA , which is typically the first large company to report earnings, swung to profit, posting earnings of $242 million or 21 cents a share, after a loss a year earlier of $191 million or 18 cents a share. Klaus Kleinfeld, CEO of the world’s largest aluminum maker, noted that growth in China appears to be making a comeback. And Europe is doing better than most expect, even as it continues to deal with ongoing debt problems. Alcoa is considered a bellwether because it supplies to a wide swath of industries. But while its earnings might say a lot about the health of the overall economy, we shouldn’t read too much into it. Just as the recent surge in the stock market doesn’t necessarily suggest the economy is in the clear, Alcoa’s return to profit says even less about how others companies will do this quarter. Earnings across the 500 companies listed on the Standard & Poor’s Index are expected to grow by a paltry 2.4%, down from 9% estimated at the start of the fourth quarter, according to FactSet, a market data research firm. The materials, financial and technology sectors will likely see the sharpest declines. If financials were excluded, overall earnings are expected to grow a mere 0.2%. MORE: Sorry, Wall Street. You’re stuck with Jack Lew For all of 2012, earnings are expected to grow about 5%, down from 9% forecasted at the start of the year. The expectations don’t get much better in the year ahead. In fact, whatever analysts are saying today should be taken lightly, as they tend to be overly optimistic following the holiday season, says John Butters, senior earnings analyst at Factset. In looking at earnings estimates over the past 15 years, analysts on average have overestimated earnings per share by about 10% between the start and end of the year. Admittedly, Butters says, unprecedented events happened during some of those years, such as the 2001 terrorist attacks and the unfolding U.S. housing crisis in 2008 and 2009. Even if that factored out, analysts still overestimated earnings. Butters expects earnings to grow 9%, with profits picking up during the last six months of the year. Earnings could grow 2.4% during the first quarter; 6% in the second; 10.9% in the third and 18% during the last three months of 2013. It’s likely though that such estimates will come down later this year as debt and deficit problems in the U.S. and Europe continue to hobble companies from getting more sales. Weak revenue growth continues to be a threat to profit growth. So in gauging how companies will fair, don’t look at the stock market. Go by analyst estimates, and take them down a few notches.