A common management practice of commercial dairy farms is grouping cows according to their nutritional needs. Having different lactation groups also implies the regrouping of animals during their lactation period. Real-time locating systems based on ultra-wideband devices provide information about the cow's position inside barns. This information can be used to infer time budgets and animal locations on a continuous basis. The present study aimed to evaluate the behavioural changes that could be induced in dairy cows when regrouping between lactation groups by using location data obtained from real-time locating systems technology. This study is based on observational data from a commercial dairy farm, where 12 regrouping events, each involving between 3 and 15 cows, were recorded without any experimental intervention. The analyses included six months of data from two lactation groups with around 100 cows in each group. The effects of regrouping on time budgets and home range were analysed by comparing changes in regrouped cows before and after the process, and by comparing regrouped cows with their matched controls. The results showed that regrouping had a slight impact on the feeding and resting times of dairy cows. In contrast, parity was associated with opposing effects on feeding and resting times. Furthermore, regrouped cows tended to cover a larger area of the barn. The extent to which regrouped cows increased their use of barn space was also affected by the number of cows regrouped simultaneously. Our analysis of location data from a commercial dairy herd provides new insights into the impact of regrouping events on cow behaviour and welfare in commercial settings.