Depending on the type of financing you'll want to be under contract to purchase a home at least 75 days prior to your lease ending. You'd like to have a little overlap of two weeks to perhaps do any work on the new place or absorb any delays. Financing will take 45-60 days and you also have to realize that your first accepted offer may have issues at inspection. Working backwards is probably the easiest way to think about it. Target the date you'd like to close and count at least 60 days back and no more than 90.