Hey all: So I contribute to a 403b, and report the amount in my W-2 using code E. Why does this not reduce my AGI on TurboTax?

Because the amount is deferred from your income in box 1 of the W-2 so you are not being taxed on the amount deferred.

It comes out of your checks pretax and have already been deducted from the wages in box 1 and you can't deduct it again.  See W2 box 1 should be less than boxes 3&5.

Oh right... box 3 is my total salary, and box 1 is my income. The difference adds up to my 403b contributions for the year. D'oh. Thank you for pointing that out.