14 U.S.C. § 2124
Promotions; pay and allowances
An officer who is promoted under section 2121 of this title shall be entitled to the pay and allowances of the grade to which promoted from his date of rank in such grade.
An officer who is promoted under section 2121 of this title shall be entitled to the pay and allowances of the grade to which promoted from his date of rank in such grade.