Costco Wholesale (NASDAQ:COST) stock has seen a nice run recently, climbing about 16% in the past three months. The rise has been driven by the company's accelerating monthly same-store sales growth as well as strong first-quarter results. Here's a look at the metrics driving investor bullishness recently.

10.5%: One of the most closely followed metrics for brick-and-mortar retailers is comparable sales, or sales trends at stores that have been open for more than a year. Costco's first fiscal quarter comparable sales were up 10.5% year over year, or 7.9% when adjusted to exclude gas inflation and changes in currencies.

A grocery cart in a wholesale store

Image source: Getty Images.

This strong growth in same-store sales encapsulates the main reason Costco has done so well recently, as the stock rose sharply when Costco previewed the quarter's strong comparable sales growth in the months leading up to its quarterly report.

Notably, Costco did say global sales growth benefited from the timing of popular shopping days that fell in the first fiscal quarter this year, compared to being counted in the second fiscal quarter last year. The timing of the quarter benefited global net sales growth during the quarter by 1.3%, management said.

Comparable sales during Wal-Mart's (NYSE:WMT) most recently reported quarter, meanwhile, climbed only 2.7%. And Target's (NYSE:TGT) comparable sales increased just 0.9% in its most recent quarter.

5.9%: Bolstering Costco's growth story, customer traffic in Q1 climbed 5.9% year over year globally, and 6.6% in the United States. But Costco noted that the aforementioned timing of key shopping days during the quarter had a positive impact on these metrics.

Wal-Mart's foot traffic for comparable stores increased 1.5% in its most recent quarter, while Target's climbed 1.4%.

13.3%: Fueled by growth in comparable sales, customer traffic, and a 4.3% bump in average front-end transactions, net sales climbed 13.3% during Q1. Sales were up about 12% when including benefits from the timing of key holiday shopping days. This is strong growth when compared to Wal-Mart and Target, which saw net sales increase 4.1% and 1.4% during their most recently reported quarters, respectively.

43.5%: One impressive achievement in Costco's sales recently is that it has been able to simultaneously post strong foot traffic growth while growing its e-commerce sales rapidly. Costco's e-commerce sales climbed 43.5% in its first quarter -- a steep acceleration compared to 21% year-over-year growth for e-commerce sales in Costco's fourth quarter of fiscal 2017.

But management said that five to 10 percentage points of its 43.5% year-over-year increase was likely due to the shift of Thanksgiving shopping days, including Cyber Monday. But as management noted, it's "still a very strong number" even after it's normalized. Indeed, even after an adjustment, it handily beats the 24% year-over-year increase in Target's digital sales during its most recently reported quarter and still marks an acceleration compared to Costco's growth in e-commerce sales in its previous quarter.

17%: Costco's first-quarter earnings per share climbed 17%, easily outpacing its 13.3% rise in net sales during this period. This outsize gain in EPS was driven primarily by a 9.8% year-over-year increase in membership fees. A recent membership fee increase, a 1% sequential increase in members, and a higher number of members paying the higher-priced Executive membership helped Costco's growth in total membership fees.

Since Costco runs its merchandise business around breakeven, growth in membership fees essentially falls directly to the company's bottom line. Fortunately, management says its recent increase to its membership rates will lead to even more positive year-over-year deltas for membership fees in the next three quarters. This is likely to drive even stronger net income and earnings-per-share growth.

Outsize growth in Costco's earnings per share has also benefited from the company's share repurchases, which have reduced Costco's total shares outstanding.

Looking to the rest of Costco's fiscal 2018, investors should look for continued momentum in comparable sales growth, as well as further acceleration in Costco's e-commerce sales. Investors should also watch for Costco's expected acceleration in earnings-per-share growth to materialize over the next three quarters.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.