I'm going to give you the overview from an FHA loan approval perspective here, just to keep it as concise as possible:
*If you're self-employed, assume you will need two years of history in every case.
*If you're a "wager earner" or receive a W-2, then a two year history is also required, but if less than 2 years is available, then:
*Provide school transcripts or military discharge paperwork. Work should be in same field as study.
*If gaps exist between employment, but 2 year history can still be obtained, gaps must be documented and explained.
*If gaps are extended (generally greater than 6 months) than new position must be in place for at least 6 months before employment can be considered stable.
Hope this helps, but let me know if not.