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Objectives To assess indirect costs (IDC) due to lost productivity in paid/unpaid labour, stratified by sex, in a national prospective observational multicentre Canadian SLE cohort.Methods Patients from six centres reported on lost productivity in paid/unpaid labour. IDC included: absenteeism (time lost from paid labour because of illness), presenteeism (degree of productivity impairment in paid/unpaid labour) and opportunity costs (additional time patients would be working in paid/unpaid labour if not ill). Opportunity costs were the difference between the time patients reported working and the time worked by an age, sex and geography-matched general population. IDC were valued using Statistics Canada wages (2024 Canadian dollars) with unpaid labour calculated using the opportunity cost method (OCM) and replacement cost method (RCM). The association of sex with IDC components was assessed (adjusted for race/ethnicity, age, disease duration, education and the Systemic Lupus International Collaborating Clinics (SLICC)/American College of Rheumatology (ACR) Damage Index) using regression modelling.Results Of the 2180 patients who participated, 90.5% were female and 67.1% were white; the mean age at diagnosis was 33.2 years and mean SLE duration was 14.7 years. Patients completed an average of 3.4 questionnaires with 51.2% of women and 47.1% of men employed at baseline. Total annual IDC were significantly higher among women using the OCM (women $35 330; men $32 016) and did not differ using the RCM (women $26 114; men $26 136). Regressions showed total IDC did not differ using either method. Unpaid labour costs were significantly higher among women (OCM: women $22 680; men $11 591 and RCM: women $13 465; men $5711) and paid labour costs were significantly higher among men (women $12 651; men $20 425). Regressions showed similar results.Conclusion IDC in SLE, particularly resulting from unpaid labour, are substantial, especially in women, where they represent up to 64.2% of total IDC versus 36.2% in men. Hence, economic analyses of novel/emerging therapies should incorporate lost productivity, including unpaid labour costs, which are of particular importance in diseases disproportionately affecting women.