Yes, you can make an additional contribution to a traditional IRA with our after-tax money (if you otherwise qualify) and this tax deduction is taken in addition to other deductions already taken; it will reduce your Adjusted Gross Income, which may result in increased refund or lower tax bill. However, if you are referring to a retirement plan that you have at work- that is already accounted for on your W-2 form and there is no additional tax break for this other than the fact that you are not taxed on your retirement plan at work (which shows on the W-2 form).
