Compared to the global average, the exit rate of old-aged Iranian labourers is significantly higher than that of middle-aged, raising the hypothesis that social security generosity pulls older workers into early retirement. We used a unique individual dataset of Iran’s Social Security Organization (ISSO), including 267, 000 newly retired in 2016 and 2018, to assess the impact of ISSO’s pension policies on employees’ retirement age. In a counterfactual evaluation design, this study first estimated the implicit tax on work continuation and then applied the Heckman two-stage selection model. The findings show that ISSO’s retirement rules determining the age of exit and benefit eligibilities significantly increase the retirement probability and simultaneously decline the retirement age. Moreover, the implicit tax on work continuation, which reflects ISSO’s benefit formula, has a significant positive effect on retirement probability. The replacement rate also has a significant negative impact on retirement age. The retirement probability in hazardous jobs is higher than in normal ones, while exemptions significantly fall the outflow age of hazardous job holders. To maintain the scheme’s sustainability, reforms have to target an increase in the statutory retirement age, a reduction in the accrual rate, the calculation of reference salary for more extended periods, and the decline of the exemption coefficient for hazardous jobs.