The median family income that is used to determine the applicant's income class is published by HUD for each MSA and statewide non-MSA annually and released by the FFIEC. To determine an applicant's income class you would divide the annual income of the applicant by the HUD EMFI for the MSA or non-MSA in which the mortgage is located and use the formula cited by JMunns.
There are many estimated family incomes released by HUD for various housing programs, so make sure you use the correct figure. It also can be found in the Census database on the FFIEC website
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