Economists typically argue population ageing generates fiscal pressures by restricting the tax base while increasing demands for social spending. Alongside other economic pressures associated with neoliberalism, this dynamic contributes to a politics of ‘enduring austerity’ that limits governments’ fiscal discretion. The politics of population ageing reflects modelling techniques, such as generational accounting (GA), which, anticipating future deficits, create demands for policy action today to address projected intergenerational inequalities. Taking Australia as a case study, this paper explores the politics of GA in public budgetary processes. While existing critiques reject GA by arguing it relies on ‘apocalyptic’ or unreliable demography, we focus on a different kind of contestation, which applies the techniques and even the categories of GA to frame different problems and promote different solutions. We identify three sites of partisan contest that refocus fiscal modelling: including the tax side of the budget equation; comparing the cost of public provision to public subsidies for private programmes; and including the costs of environmental damage. At each site, the future-orientated logic of GA is mobilised to contest the policy implications of austerity. This complicates analysis that financialisation and neoliberalism necessarily ‘de-politicise’ policy by removing state discretion. Instead, we identify an increasingly important, if technocratic, form of political contestation that offers the possibility to promote more egalitarian responses to population ageing.