Background: Unpaid work is unequally distributed between men and women, and is associated with mental health. However, the nature of this relationship is poorly understood. We sought to determine whether a tipping point exists beyond which unpaid work adversely affects mental health, and whether this differs by gender.

Methods: We used data from the Household, Income and Labour Dynamics in Australia (HILDA) survey (2001–2023), a nationally representative prospective panel study, and drew on an analytic sample of employed Australians aged 25–64 years (n=162,035 observations). To address reverse causality between unpaid work (total weekly hours of household tasks, childcare, and caring responsibilities) and mental health (MHI-5 subscale of SF-36), we applied a two-stage least squares instrumental variable (IV) estimator, using home ownership and number of bedrooms as instruments.

Results: An inverted U-shaped relationship between unpaid work and mental health was observed for the overall sample and for men, with mental health initially improving as unpaid hours increased, but deteriorating beyond a threshold. The tipping point was 32.3 hours/week for the overall sample and 28.6 hours for men. The curve was flatter and non-significant for women, with a higher estimated tipping point of approximately 32.6 hours.

Conclusion: The mental health impacts of unpaid work depend on intensity and are patterned by gender. Men's mental health was more responsive to increases in unpaid work and deteriorated at lower levels. Women's mental health was less sensitive, consistent with acculturation to higher baseline unpaid workloads which are structured by gender normative divisions of labour.