(a) The present value of a deferred annuity equals the present value of the deferred annuity without credit for the NAFI service as of the deferred annuity date discounted for interest to that date.

(b) The present value of the deferred annuity without credit for the NAFI service as of the deferred annuity date equals the retiree's monthly annuity without credit for the NAFI service as of the deferred annuity date times the present value factor for the retiree's age on that date.

(c) The present value under paragraph (b) of this section is discounted for interest by dividing that amount by a factor equal to the value of the exponential function in which—

(1) The base is one plus the assumed interest rate under 5 CFR part 841, subpart D, on the commencing date of the retiree's immediate annuity, and

(2) The exponent is one-twelfth of the number of months between the commencing date of the retiree's immediate annuity and the deferred annuity date.