• The poverty thresholds, and
• The poverty guidelines.

The poverty thresholds are the original version of the federal poverty measure.  They are updated each year by the Census Bureau (although they were originally developed by Mollie Orshansky of the Social Security Administration).  The thresholds are used mainly for statistical purposes — for instance, preparing estimates of the number of Americans in poverty each year.  (In other words, all official poverty population figures are calculated using the poverty thresholds, not the guidelines.)  Poverty thresholds since 1980 and weighted average poverty thresholds since 1959 are available on the Census Bureau’s Web site.  For an example of how the Census Bureau applies the thresholds to a family’s income to determine its poverty status, see “How the Census Bureau Measures Poverty” on the Census Bureau’s web site.

The poverty guidelines are the other version of the federal poverty measure. They are issued each year in the Federal Register by the Department of Health and Human Services (HHS).  The guidelines are a simplification of the poverty thresholds for use for administrative purposes — for instance, determining financial eligibility for certain federal programs.  The Federal Register notice of the 2009 poverty guidelines is available.

The poverty guidelines are sometimes loosely referred to as the “federal poverty level” (FPL), but that phrase is ambiguous and should be avoided, especially in situations (e.g., legislative or administrative) where precision is important.

Key differences between poverty thresholds and poverty guidelines are outlined in a table under Frequently Asked Questions (FAQs). See also the discussion of this topic on the Institute for Research on Poverty’s web site.