Thanks. I think in some community property states (TX?), the survivor gets step-up on 100% of the house. And yes, I'm planning to use the property tax appraisal. They are generally fairly close to FMV in Texas, or at least that's the intent.
Also, I would think I can only count improvements after the step-up date, but not sure. So again, since I've never done this before, I think it would be advisable to use the guidance in Premiere.
I agree in most community property states, you will get step up on full basis not 50%. As far as valuation, and improvements you have two different determinations. Valuation is usually Fair Market Value at date of passing--not all state's use FMV for assessed value (usually some percentage) so check what your state's property tax rules are--county assessor can advise.
When you are dealing with improvements, prior to date of death it does not matter as the step up to fmv establishes the new basis going forward. Improvements following death may be capital or expense of sale both deductible if done usually in the immediate 12 months following death.