In such an event, section 72(d) provides that all amounts received as an annuity under the contract during a taxable year to which the Code applies shall be excluded from gross income until the total of the amounts excluded under that section plus all amounts excluded under prior income tax laws equals or exceeds the consideration contributed (or deemed contributed) by the employee. The excess, if any, and all amounts received by any recipient thereafter (whether or not received as an annuity), shall be fully included in gross income. See paragraph (b) of this section.
See also paragraph (d) of § 1.72-14 .
26 C.F.R. §1.72-13