Thanks to Costco's (NASDAQ:COST) practice of reporting monthly sales results, investors already know the retailer will likely announce robust revenue growth when it reports earnings on Thursday, Oct. 3. The warehouse giant revealed back in early September that comparable-store sales were up 5% through most of the fiscal fourth quarter, which puts it comfortably ahead of rival Walmart (NYSE:WMT) in the market share race.

That doesn't mean Thursday's report won't be packed with important information for investors, though. Let's look at a few of the metrics Costco will announce this week that could set the stage for the stock's performance over the next few months.

A warehouse shopper walks through an aisle

Image source: Getty Images.

1. Customer traffic

Costco's roughly 5% sales uptick in recent months has kept its expansion pace steady and also continued the performance gap with peers like Walmart, which posted a 3% increase in its last quarter. Yet the warehouse giant reported a significant slowdown in customer traffic last quarter, with growth falling to 3.4% compared to nearly 6% in the prior quarter.

At the time, CFO Richard Galanti told investors it wasn't clear whether the decline was part of a bigger trend in the industry or just a temporary blip. This week's report will go a long way toward clearing that up, depending on whether traffic growth continues decelerating or begins recovering again. In either case, Costco is likely to express confidence in its market position. "We think...our value proposition is as strong, if not stronger, than it's ever been out there," Galanti said back in late May.

2. Gross profit margin

As important a factor as it can be in supporting earnings growth, gross profit margin just isn't Costco's strong suit. The warehouse club prefers to generate most of its profits through membership fees while selling its products at close to break-even. Still, gross margin ticked up last quarter thanks to the combination of lower costs and the leverage Costco is winning from its rising sales base.

The chain is likely to direct nearly all of those gains back toward improving the shopping experience, so investors should keep their expectations in check. Yet even a small sustained boost on this metric could power accelerating earnings growth heading into a new fiscal year.

3. Renewal trends

Costco is a membership club first and a retailer second. Its subscriber trends play a bigger role, then, in predicting its future growth and in supporting its current earnings strength. That fact means renewal trends are among the most important metrics Costco reports each year.

Renewal rates held steady at about 90% in each of the last two fiscal years but are on track to rise to a record 91% in the year Costco is closing out this week.

This success filters through the business in a few ways. The most direct path is higher membership fees since more subscribers are renewing at the chain's rising annual fee rate. Engaged shoppers are more likely to upgrade to executive membership status, too, while supporting its increasing customer traffic metric. Most importantly, a healthy renewal rate confirms that Costco is providing plenty of value to warehouse shoppers even as retail spending shifts more toward online spending.