google "above line deduction. "

In 1040, adjusted gross income  (AGI) is an important line. 

Standard/Itemized deduction comes after AGI.   It's called below the line. 

Some deductions are called "above-line deductions" because they are removed from your income completely, such as business expense, loan interest etc.  

SS tax formula is determiend "above the line", that is, before your AGI is determined.  Therefore standard/itemized deduction does not come into play.