Retirement tax questions

That comes out of your paycheck pre-tax (meaning before taxes) it has already been deducted from your gross wages in box 1 on your W2 and you can't deduct it again. Notice that box 1 is less than boxes 3 & 5.  You only enter it from the W2.   That's why you have to wait for your W2.  It will be different than your paystubs.