Most companies that have already reported have topped expectations: As of Friday, about 16.5 percent of S&P 500 companies have announced their quarterly earnings, with 81.5 percent of them topping expectations, according to FactSet.
But even with the seemingly good news, the 500-stock index was up around just half a percent last week. That has been attributed to several reasons, including guidance revisions and rising interest rates, among others.
First-quarter results across S&P 500 companies were last estimated by Thomson Reuters I/B/E/S to increase by 20 percent compared to one year ago.
— CNBC's Fred Imbert contributed to this report.