Question:   Can I take an IRA deduction for the amount I contributed to a 401(k) plan last year?

Answer:   In general, an amount contributed to a 401(k) account cannot be used as an IRA deduction.  However, if the 401(k) plan has a deemed IRA feature, contributions to the deemed IRA may be deductible in accordance with the IRA contribution rules.

A pre-tax 401(k) contribution is already excluded from your Federal (and most state and local) taxable income, as it is not included in box 1 taxable wages of your W-2 form. Deemed IRA contributions are included in box 1 and you use the normal IRA contributions rules to determine their deductibility.