If your employer handled your 401(k) contributions correctly in preparing your W-2, your contribution was considered. The proper handling is to reduce your gross pay by the amount of your contributions. You can sometimes tell if this was done by looking at the amounts in Box 1 and Box 3. If Box 3 is larger, it is likely that the employer handled this properly. If there are any questions, you can contact the Human Resources department at your employer to see how this was done. Note that there are other reasons that Box 3 may be larger than Box 1 but 401(k) is by far the most prevalent one.
