On screen 29 business use of home, when do you check the box to Allocate all mortgage interest and real estate taxes as excess when claiming standard deduction?

[LSTAX]

Only when the standard deduction is used or should you always check the box?  It looks like checking the box gives incorrect calculation if itemizing.

In this case, they can itemize deductions but SALT limitation $10,000 applies.  I have the 8829 worksheet line 11 going to form 8829 line 17 (excess real estate taxes under direct column) and line 7 going to schedule A line 5b.  If I check the box to allocate all mortgage interest and real estate taxes as excess, tax goes up because mortgage interest also moves down to line 16 excess mortgage interest.

 Are we only to check the box if they are taking standard deduction.  I thought we should check the box either way and Lacerte would know whether or not they are claiming the standard deduction.

Thank you

[IntuitAlicia]

Are you producing any diagnostics? The Schedule A and 8829 instructions include some additional detail about these items that you may find helpful.