This study assessed the subjective well‐being and perceived stress of unpaid carers of disability benefit claimants. A total of 129 carers from the UK were surveyed between July and September 2017, using a cross‐sectional design. Carers, who provided unpaid support to sick or disabled friends, family or neighbours in a non‐professional capacity, reported here as unpaid carers, were asked to complete a web‐based questionnaire comprising of the Perceived Stress–10‐item Scale (PSS‐10), the Personal Wellbeing Index–Adult (PWI‐A), sociodemographic characteristics, the time they spent caring per day and the number of Personal Independence Payment and Work Capability Assessment interviews prepared for and attended by the person they cared for. Hierarchical regression analyses were performed to assess the effects of the number of benefit assessments on stress and well‐being scores, controlling for carers' sociodemographic characteristics and the time they spent caring. Analyses revealed that the number of times that claimants were exposed to benefit assessments significantly and negatively predicted unpaid carers' well‐being and was positively related to their stress levels. After controlling for sociodemographic characteristics and hours supporting per day, benefit assessments predicted 8.1% of perceived stress and 4.3% of well‐being variance. Being a female unpaid carer of a disability benefit claimant negatively predicted 7.5% of well‐being variance. The results offered unique evidence of the negative psychological effects of disability benefit assessments upon unpaid carers, while adding to the evidence of female carers facing increased risks of psychological distress.