(a)(1)(A) Except as provided in paragraph (2), or subsection (b), (c), or (d), the annuity of an annuitant under this subchapter—

(i) for the period beginning on the date on which such annuity commences, or is restored (as described in section 8455(b)(2) or (3)), and ending at the end of the twelfth month beginning on or after such date, shall be equal to 60 percent of the annuitant’s average pay; and

(ii) after the end of the period referred to in clause (i), shall be equal to 40 percent of the annuitant’s average pay.

(B) An annuity computed under this paragraph—

(i) shall not, during any period referred to in subparagraph (A)(i), be adjusted under section 8462; but

(ii) shall, after the end of any period referred to in subparagraph (A)(i), be adjusted to reflect all adjustments made under section 8462(b) after the end of the period referred to in subparagraph (A)(i), whether the amount actually payable to the annuitant under this section in any month is determined under this subsection or otherwise.

(2)(A) For any month in which an annuitant is entitled both to an annuity under this subchapter as computed under paragraph (1) and to a disability insurance benefit under section 223 of the Social Security Act, the annuitant’s annuity for such month (as so computed) shall—

(i) if such month occurs during a period referred to in paragraph (1)(A)(i), be reduced by 100 percent of the annuitant’s assumed disability insurance benefit for such month; or

(ii) if such month occurs other than during a period referred to in paragraph (1)(A)(i), be reduced by 60 percent of the annuitant’s assumed disability insurance benefit for such month;

except that an annuity may not be reduced below zero by reason of this paragraph.

(B)(i) For purposes of this paragraph, the assumed disability insurance benefit of an annuitant for any month shall be equal to—

(I) the amount of the disability insurance benefit to which the annuitant is entitled under section 223 of the Social Security Act for the month in which the annuity under this subchapter commences, or is restored, or, if no entitlement to such disability insurance benefits exists for such month, the first month thereafter for which the annuitant is entitled both to an annuity under this subchapter and disability insurance benefits under section 223 of the Social Security Act, adjusted by

(II) all adjustments made under section 8462(b) after the end of the period referred to in paragraph (1)(A)(i) (or, if later, after the end of the month preceding the first month for which the annuitant is entitled both to an annuity under this subchapter and disability insurance benefits under section 223 of the Social Security Act) and before the start of the month involved (without regard to whether the annuitant’s annuity was affected by any of those adjustments).

(ii) For purposes of applying section 224 of the Social Security Act to the assumed disability insurance benefit used to compute the reduction under this paragraph, the amount of the annuity under this subchapter which is considered shall be the amount of the annuity as determined before the application of this paragraph.

(3) Section 8462 shall apply with respect to amounts under this subsection only as provided in paragraphs (1) and (2).

(b)(1) Except as provided in subsection (d), if an annuitant is entitled to an annuity under this subchapter as of the day before the date of the sixty-second anniversary of the annuitant’s birth (hereinafter in this section referred to as the annuitant’s “redetermination date”), such annuity shall be redetermined by the Office in accordance with paragraph (2). Effective as of the annuitant’s redetermination date, the annuity (as so redetermined) shall be in lieu of any annuity to which such annuitant would otherwise be entitled under this subchapter.

(2)(A) An annuity redetermined under this subsection shall be equal to the amount of the annuity to which the annuitant would be entitled under section 8415, taking into account the provisions of subparagraph (B).

(B) In performing a computation under this paragraph—

(i) creditable service of an annuitant shall be increased by including any period (or periods) before the annuitant’s redetermination date during which the annuitant was entitled to an annuity under this subchapter; and

(ii) the average pay which would otherwise be used shall be adjusted to reflect all adjustments made under section 8462(b) with respect to any period (or periods) referred to in clause (i) (without regard to whether the annuitant’s annuity was affected by any of those adjustments).

(c) Except as provided in subsection (d), the annuity of an annuitant under this subchapter shall be computed under section 8415 if—

(1) such annuity commences, or is restored, beginning on or after the redetermination date of the annuitant; or

(2) as of the day on which such annuity commences, or is restored, the annuitant satisfies the age and service requirements for entitlement to an annuity under section 8412 (other than subsection (g) of such section).

(d)(1) The annuity to which an annuitant is entitled under this section (after the reduction under subsection (a)(2), if applicable, has been made) shall not be less than the amount of an annuity computed under section 8415 (excluding subsection (h) of such section).

(2) In applying this subsection with respect to any annuitant, the amount of an annuity so computed under section 8415 shall be adjusted under section 8462 (including subsection (c) thereof)—

(A) to the same extent, and otherwise in the same manner, as if it were an annuity—

(i) subject to adjustment under such section; and

(ii) with a commencement date coinciding with the date the annuitant’s annuity commenced or was restored under this subchapter, as the case may be; and

(B) whether the amount actually payable to the annuitant under this section in any month is determined under this subsection or otherwise.