Section 847.905 - How is the present value of an immediate annuity with credit for NAFI service computed?(a) OPM will determine the present value of the immediate annuity including service credit for NAFI service by multiplying the monthly annuity rate as of the commencing date of the annuity by the present value factor for the retiree's age on that date.(b) The monthly annuity rate under paragraph (a) of this section for CSRS and CSRS Offset retirees equals the monthly rate of annuity otherwise payable under 5 U.S.C. chapter 83, subchapter III, including all reductions provided under that subchapter.(c) The monthly annuity rate under paragraph (a) of this section for FERS retirees equals the monthly rate of annuity otherwise payable under 5 U.S.C. chapter 84, subchapter II, including all reductions provided under that subchapter.