are paid to, or includible in gross income of, the payee within one taxable year of the payee by reason of the employee's death or other separation from the service, or death after such separation from the service, such total payments, to the extent they exceed the net amount contributed by the employee, shall be considered a gain from the sale or exchange of a capital asset held for more than six months. The "net amount contributed by the employee" is the amount actually contributed by the employee plus any amounts considered to be contributed by the employee under the rules of sections 72(f), 101(b), and paragraph (d) of § 1.403(a)-1 , reduced by any amounts theretofore distributed to him which were excludable from his gross income as a return of employee contributions. For example, if under an annuity contract purchased under a plan described in this section, the total distributions payable to the employee's widow are paid to her in the year in which the employee dies, in the amount of $8,000, and if $5,000 thereof is excludable under section 101(b), and if the employee made contributions of $600 and had received no payments, the remaining amount of $2,400 will be considered a gain from the sale or exchange of a capital asset held for more than six months.
26 C.F.R. §1.403(a)-2