Pension gaps between men and women result from a combination of unequal careers, changes to the legislation, and changes in retirement behaviour. This article analyses the observed pension gaps between men and women retiring in 2009, and the future pension gaps between men and women retiring in 2029 using projections based on CNAV’s Prisme model. The aim is to highlight potential changes in the inequality in pensions between men and women retiring in 2029 compared with those retiring in 2009. In order to identify the explanatory factors behind gaps, the study covers the base pensions of people who are retiring on a general scheme pension only. The emphasis is on the differences in pension between homogeneous populations, in particular in terms of age at retirement, in order to clarify the respective roles of careers and compensation mechanisms in the calculation of the pension. Among general-scheme retirees who only ever worked as private-sector employees over the course of their careers, women’s base retirement pensions in 2009 were 33% lower than men’s. The gap is expected to narrow to 24% in 2029, according to CNAV projections. In 2009, the level of salaries was important but career breaks and consequently different career lengths reinforce pension gaps, in particular for women who retire at 65. By comparing the results for 2029 with those for 2009, the percentage of men retiring on full pensions awarded for length of career fell sharply. Differences in career length are also diminishing partly as a result of the corrective mechanisms provided for under the current legislation (the assurance vieillesse des parents au foyer/AVPF, or pension contributions paid for parents who receive certain family benefits; the majoration de durée d’assurance/MDA, which awards up to 3 years in additional quarters per child, and quarters counted for childbirth). Consequently, in 2029, the main cause of differences in pension between men and women who retire at the same age are likely to be residual pay gaps during their working lives.