When aluminum giant Alcoa releases its results on Monday, it will mark the unofficial start of the heaviest reporting season for S&P 500 companies.

The final scoreboard is expected to show a 9.1% earnings drop for the quarter, according to FactSet senior earnings analyst John Butters.

But the actual decline will likely be smaller, he said. Analysts have ended up being too pessimistic about most quarters since Q2 2013.

Still, earnings would be negative for a third straight quarter.