Costco (NASDAQ:COST), the world's second-biggest retailing chain, will post its quarterly earnings results after the market closes on Wednesday, March 7. Let's take a look at a few trends investors will be watching in the report.

Robust sales growth

Costco is one of just a few major retailers that still reports monthly sales numbers. As a result, we already know some tantalizing details about its holiday season. The warehouse giant's comparable-store sales shot up by 9% in December, executives said recently, which means Costco likely continued a market-thumping growth streak that has left rivals like Walmart (NYSE:WMT) and Target (NYSE:TGT) far behind. Walmart's comps were 2.6% over the holiday season and Target's expansion rate was just over 3%.

Woman with shopping cart browsing the aisles at a warehouse retailer.

Image source: Getty Images.

Looking beyond the headline comps number, investors will be watching Costco's customer traffic figure for signs that the retailer is still snapping up market share. That metric jumped a blistering 5.9% in the fiscal second first quarter, but anything at or above 4% would be great news for the business. Keep an eye on e-commerce sales, too, since they had been expanding at a 40% rate heading into the holidays but likely slowed somewhat, but perhaps not as dramatically as they did at Walmart.

Profit bounce

Costco generates close to zero profits from its product sales, with most of its earnings coming from subscription sales instead. That helps explain why Wall Street celebrated when the company announced an increase in its membership rate last year. The hike helped net income spike by 17% in the most recent quarter to outpace Costco's 13% revenue increase. It also put further distance between Costco and its more retailing-focused peers.

COST Net Income (TTM) Chart

COST Net Income (TTM) data by YCharts.

Investors can expect the new subscription rate to continue lifting earnings results as the membership base transitions to the higher-priced plans. In fact, executives said the impact would be even more pronounced in the fiscal second quarter.

Costco's fees are also trending higher as a result of new store openings and the deeper penetration of executive membership plans that today account for 38% of the membership base, up from 25% a decade ago. The combination of these positive trends likely accounts for the fact that consensus estimates call for Costco to post a 25% profit improvement for the quarter as earnings rise to $1.46 per share.

Steady renewal rates

While important metrics like customer traffic have rebounded over the last few quarters, one critical number has refused to budge recently. Costco's membership renewal rate held steady at 90% last quarter even though management had predicted it would begin climbing back toward 91% now that the disruption from its credit card switchover has passed.

Executives expressed confidence back in December that the issue wasn't a result of shoppers gravitating away from its stores and choosing to do more shopping at, for example, e-commerce focused rivals. They had plenty of support for that argument, including robust shopper traffic. Still, if renewal rates hold steady again in the fiscal second quarter, or worsen slightly, it might suggest Costco has a looming market share challenge on its hands.

Yet the most likely scenario is that the retailer will announce healthy renewal rates that reflect its success at delivering low prices and a high-quality product selection to its membership base over the last few months.

Demitrios Kalogeropoulos owns shares of Costco Wholesale. The Motley Fool recommends Costco Wholesale. The Motley Fool has a disclosure policy.