Affordable housing is a term used to describe dwelling units whose total housing costs are deemed "affordable" to those that have a median income. Although the term is often applied to rental housing that is within the financial means of those in the lower income ranges of a geographical area, the concept is applicable to both renters and purchasers in all income ranges. This article focuses on the affordability of owner-occupied and private rental housing as social housing is a specialised tenure.

In the United States and Canada, a commonly accepted guideline for housing affordability is a housing cost that does not exceed 30% of a household's gross income. Housing costs considered in this guideline generally include taxes and insurance for owners, and usually include utility costs. When the monthly carrying costs of a home exceed 30–35% of household income, then the housing is considered unaffordable for that household.

Supply and demand

In the United States, a key element in determining affordable housing is acceptable commuting time/distance. In Southern California, for example, a household's inhabitants must decide whether to pay more for housing to keep commuting time and expense low, or to accept a long and/or expensive commute in order to obtain "better" housing.