Given the urgent need to promote climate-friendly behaviours, the implementation of carbon footprint calculators with actionable recommendations is increasing. This study analysed data from >7000 users of a Japanese carbon footprint calculator to investigate the characteristics and factors affecting voluntary commitment to decarbonisation actions and the gaps in achieving the 1.5-degree mitigation target. The results showed voluntarily committed actions were insufficient to meet the 2030 personal carbon footprint target, with only 31 %, 18 %, and 7.3 % of users potentially achieving targets in the domains of housing, mobility, and goods/services, respectively. The seven user segments that were identified exhibited very different levels of engagement. For example, ‘lifestyle change enthusiasts’ committed to as many as 25 actions, corresponding to an equivalent of 2.8 tCO₂e of footprint reduction, while ‘curious bystanders’ rarely committed to any actions. Demographically, younger and male users tended to prioritise high-impact actions, whereas female users and users aged 50–60 years old were more likely to commit to a range of actions. Notably, actions requiring substantial financial investment had an 8 % lower commitment probability, and ‘shift’ actions were 6 % less preferred than ‘avoid’ actions”. These findings contribute to a deeper understanding of the considerable gap between self-committed actions and mitigation targets, and suggest that more effective use of footprint information could facilitate greater engagement. Tailored strategies could better motivate the ‘curious bystanders’ segment and encourage female and older users to focus on high-impact actions.