My client has a sch C home office. when i enter data: mortgage interest/ property taxes. should i share that with the Sch A. ?This client lives in CA

[MarlaE]

I want to choose the best option without a huge unallowed $ amount to carryover if it can be better utilized in the current tax return.

[PhoebeRoberts]

Yes, but there's some manual side calculating you need to do using the Worksheet for Line 11 from the Form 8829 instructions. For most people with state income taxes in excess of $10k, you'll take the HO portion of the RE taxes and enter them as Excess Real Estate Taxes in the Direct Expenses input area.

If you don't want a carryover, elect to use the simplified method. Whether that's a better income tax answer or not is determinable by comparing the tax one way with the tax the other.