Housing is the largest capital asset many families own and thus can be used to provide financial flexibility, for example, as collateral against a personal loan. Housing wealth is the net asset value of an owner occupied dwelling calculated as the market value, minus the mortgage debt. Housing costs are usually the largest item of household expenditure. To adjust for this, disposable income is sometimes calculated after housing costs have been accounted for. When interest rates rise, households with mortgages can face a decline in after-housing disposable income.