The COVID-19 pandemic has exposed how our global societies rely upon the care and support of informal (unpaid) caregivers: in the UK alone, there are an estimated 6.5 million informal carers. The caring role is not just precarious, it is often associated with high levels of stress, poor/deteriorating health and crisis points (hospitalisations, worsening of health). Fittingly, there has been much research in recent years focusing on mental health supports. A lesser explored area is physical health and physical activity. To address this, we conducted a real-world feasibility, usability and acceptability study of a novel codesigned digital health app for caregivers to improve levels of physical activity. Our study was designed to test the prototype app use for three weeks, following participants across questionnaires/in app data/qualitative data. Our findings (from 27 caregivers) highlights key knowledge gaps around physical activity—national guidelines were not reaching populations studies and behavioural change techniques hold promise to help support caregivers in the longer term. Our collective results support the acceptability, usability and feasibility of the Carefit app and warrant further investigation.