My mother put my name on her house deed before her death.
Lots of possibilities with that statement.
If she "added" your name to the deed along with hers, then you are 50% owner of the house. Your cost basis of your 50% is whatever your mother originally paid for the house, plus 50% of the cost of any property improvements done to the house before she deeded it to you.
At the time of her passing you would then inherit her 50%, meaning you get an increase in basis of "only" her 50%.
If your mother deeded the entire property to you (thus taking her name off the deed and replacing it with your name) then you have not inherited anything upon her passing. your cost basis is whatever your mother originally paid for the property, plus the cost of any property improvements done prior to her replacing her name on the deed, with yours.
In both cases above, a gift tax return most likely needed to be filed in the same tax year as the deed was changed. (IRS Form 709).
If you don't know how deeding was done, or if a gift tax return was "in fact" filed or not, then you should seek professional help for dealing with this. Especially if your state also taxes personal income.
Either way things are, if you sold the property at a gain, you will most definitely have a taxable gain, since the home was never your primary residence during the last 5 years you had any degree of ownership in the property.
