If my IRA contributions are shown on my W-2 can I input those numbers into the Traditional IRA Contributions portion of the Deductions & Credits?

[LindaA]

No. Contributions to your employer-sponsored retirement plan are already pre-tax, so you cannot claim them as a deduction on your tax return. If you contributed to your employer-sponsored plan, the information was reported on your W-2 in box 12. The code depends on the type of the plan:

• D: 401(k) plan
• E: 403(b) plan
• F: 408(k)(6) plan
• G: 457(b) plan
• S: 408(p) salary reduction SIMPLE retirement account
• H: 501(c)(18)(D) plan

Note that an Individual Retirement Arrangement (IRA) is a retirement plan that you set up yourself and not an employer-sponsored retirement plan, such as a 401(k) plan.

[ToriC90]

But what if you have both an employment based retirement plan that is pre-taxed and a roth elective deferral? I do not believe my roth elective deferral is pre-tax but it is reported on my w2. 

[SteamTrain]

@ToriC90 

No..not that either.

Those paycheck withholdings are not IRA or ROTH IRA contributions. The contributions done with your paycheck and noted in box 12, are entered only with your W-2 and nowhere else.

The IRA/RothIRA contributions section  on the Deductions& Credits page is ONLY for extra contributions you make yourself outside of any employers plan, to some separate account you may have set up..  

Note too that the max amount allowed to be contributed at the employer is usually ~2.5x   greater than for the IRA/Roth IRA contribution section..