Previous research finds that members of the working class have a higher risk of early retirement compared to professionals because they are pushed into early retirement. This indicates that not all workers can respond to incentives to extend their working life. Yet, little previous work has been conducted to quantify systematically the extent to which push factors explain why members of the working class have a higher risk of early retirement compared to professionals. Using longitudinal data on Danish workers, the results suggest that members of the working class have an increased risk of early retirement compared to professionals, but poor health, previous spells of unemployment and low job quality mediate a large part of this effect. Among men, the push factors mediate 57 and 86 per cent of the effect of social class on early retirement for skilled manual and unskilled manual workers, respectively. Among women, the push factors mediate 43 and 55 per cent of the effect of social class on early retirement for skilled manual and unskilled manual workers, respectively. Overly physical work demands is the most important mediator, which explains between 23 and 31 per cent of the total effect of belonging to the working class on early retirement. Moreover, the magnitudes of the indirect effects of the push factors depend on the particular pathway into retirement.