Accurate measurement of housing affordability is needed to decide if a family qualifies for assistance in housing or for a mortgage to purchase privately. While the 30% rule may be used for the latter, banks and lending agencies might require a much higher Qualifying Income before approving a mortgage. The Royal Bank of Canada Housing Affordability Measure describes a qualifying income as "the minimum annual income used by lenders to measure the ability of a borrower to make mortgage payments. Typically, no more than 32% of a borrower’s gross annual income should go to ‘mortgage expenses’ — principal, interest, property taxes and heating costs."