Abstract Purpose The purpose of this paper is to identify how fashion and cosmetics e-stores compete and grow to help e-commerce managers set the corresponding marketing strategy. It describes the relevance of customer acquisition and retention to market share as the essential performance metrics. Design/methodology/approach An empirical generalization approach where patterns in data appearing across studies are described by a mathematical or graphical method is used. To do that, the authors observed real transactional data and the effect of how e-stores benefit from new and returning customers and gain a larger market share. The authors have analysed behavioural data from nearly 124,000 e-commerce customers in two highly popular product categories (fashion and cosmetics) in the size of 10,000,000 euros in sales or more. Findings Fashion and cosmetics e-stores with more market penetration tend to have a higher market share measured both by the number of total purchases and the number of sales in euro. In other words, market penetration is a solid predictor of market share in all circumstances. Interestingly, no significant difference in loyalty has been observed in relation to market share growth except in the situation where the market partition was excluded from the product category. Research limitations/implications The businesses under study derived only from one country and only two product categories were observed. Thus, there is a potential limitation in generalizing the findings to the whole e-commerce market from a geographical and category perspective. The length of the observation period may also play a role as a longer period increases the chance of repeat buying. Practical implications E-commerce managers can gain long-term market share growth mainly via higher market penetration (acquisition of new customers) and should avoid misleading overfocus on loyalty tactics (retention of current customers). The study also provides important benchmarks for e-commerce businesses in the fashion and cosmetic categories. Originality/value In the market share growth literature, only a handful of studies focus on stores and not on products. Moreover, there is a dominance of fast-moving consumer goods categories. Surprisingly, studies analysing ever-growing e-commerce markets are scarce. Thus, this research is original because it describes, using empirical data, how brands online, at the store level and within the fashion and cosmetics category, grow their market share. It is also one of the few studies that work with real business transactional data.