Household projections combine different inputs: on the one hand, population projections by age and sex, and on the other hand hypotheses about changes in cohabitation behaviour at a given age and sex.

Demographic hypotheses are based on three components of population variations : fertility, mortality and migrations.

Hypotheses about changes in cohabitation behaviour are formulated by the statistical service of the Ministère de la transition écologique et de la cohésion des territoires (SDES) and based on observed trends over the last decade (2008-2018). These hypotheses split individuals of a given age an sex, over the projection period, between living in ordinary housing or not (outside a household) and belonging to a household with different living arrangements (children within a household, single parents, single people, couples, other households of size 2, other households of size 3 or more).
Several scenarios are considered for changes in cohabitation behaviours, including a 'central' scenario that perpetuates recent trends (at the same rate as the last decade: 2008 to 2018 until 2030, then at half the rate until 2050).