15 years ago, my parents jointly deeded their house to me and retained a life estate interest as recorded in the deed.  Seven years ago, my father died.  My mother continued to live in the house until this past April when she passed away.  My question is how do I determine my cost basis in the house for Federal income tax purposes.  Is my basis soley based on the market value when my Mother died, or does my father's death factor in at all.  My father left all of his possessions to my mother upon his passing, although there was no specific reference to the house.