This study models the economic costs of informal caring for people with back pain, using a microsimulation model, Care&WorkMOD, from 2015 to 2030. Care&WorkMOD was based on 3 national Australian Surveys of Disability, Ageing and Carers (2003, 2009, 2012) data sets for individuals aged 15 to 64 years. Estimated national income loss due to caring for people with back pain was AU$258 million in 2015, increasing to $398 million in 2030 (54% increase). Lost income tax revenue to the Australian government due to informal care of people with back pain was estimated to be AU$78 million in 2015, increasing to AU$118 million in 2030 (50% increase), and additional welfare payments were estimated to rise from $132 million in 2015 to AU$180 in 2030 (36% increase). Larger growth in lost income, compared with the increase in welfare payments, means that there would be an increasing income gap between those out of the labour force providing informal care and noncarers who are in the labour force, leading to increased inequality. Informal carers are defined as providers of informal, unpaid assistance to someone with a health condition, for at least 6 months. Informal carers of people with back pain who are out of the labour force incur substantial economic costs. Furthermore, back pain is a large economic burden on national governments. Policies addressing back pain prevention and treatment, and supporting carers, may offset government welfare expenditure, while improving the socioeconomic well-being of carers and patients.