Pension reform, which was aborted in 2020 following the Covid-19 crisis, has been part of President Macron’s second-term programme since the electoral campaign of Spring 2022. It has been regularly confirmed as being on the government’s agenda, despite the absence of an absolute parliamentary majority. Widely regarded as essential for coping with the future funding difficulties created by an ageing population, the details of that reform are the subject of much debate and lively discussion between the social partners in France and this will inevitably continue over the coming months. In this context, the studies carried out this spring by France Stratégie, under Pierre-Yves Cusset’s co-ordination, to gauge the impact of demographic ageing on welfare protection in France, represent an essential contribution to debates. This article presents the method of these studies and the main lessons to be drawn. First of all, it is important to remember that this is about measuring the pressure that an ageing population — and that factor alone — exerts on social accounts, working on the basis of the central scenario of the demographic projections published by INSEE. On this basis, were expenditure and income per inhabitant to remain unchanged in each age group, the social welfare deficit would have been 110 billion euros in 2019 if France had had the age pyramid that is anticipated for 2040 (as opposed to the 13 billion euro surplus actually registered in 2019): a massive shock, though Cusset shows that it is more or less of the same order of magnitude as the shock France has already experienced over the last two decades. Moreover, this mechanical impact of ageing is appreciably less great in France than among its European neighbours (particularly Germany and Spain), thanks to the country having a population with a younger age-profile. Though the demographic shock to be expected over the next 20 years is far from negligible (it is estimated at around 5 percentage points of GDP), it may, then, be less difficult to overcome than is generally feared — thanks to the effects of past reforms that are yet to be felt, and provided that there is a modicum of economic growth.