Does anyone know which box 12 do I enter for HSA contributions? I have 12a-c.

[VolvoGirl]

You can use any box 12a, 12b, 12c etc.  Those are just the  box labels.  You need  to enter the CODE and Amount.  Aren't you entering from the actual W2?  Don't  use  your last paystub .   You need the actual W2.  The W2 might not match your paychecks.  There are several pretax items that can affect it.