From the EOB
Last day of work is usually the date of retirement. Suppose an employee’s last day of work is December 31. Is his date of retirement after that date, which would push retirement into the next calendar year and postpone the RBD by one year as well? According to the IRS, the determination of retirement date is one of facts and circumstances, but normally the last day of work is the date of retirement. The IRS explained its position in a Q&A session with the Taxation section of the American Bar Association held on May 9, 2003. See Q&A-12. However, if the employee returns to work on a sporadic basis, or there is other evidence of retirement occurring on a later date, then there may be a later retirement date for RBD purposes.