Wal-Mart Stores Inc. posted a 17% rise in fiscal second-quarter net income, topping raised expectations and prompting the company to boost its fiscal-year target.

But the company gave cautious initial guidance for the current quarter, largely falling below analysts’ estimates, as the world’s largest retailer expresses some caution about how U.S. shoppers will fare in coming months now that a boost from federal stimulus checks is running its course.