Section 591.238 - How do agencies pay COLAs and post differentials?(a) Agencies pay COLAs and post differentials as a percentage of an employee's hourly rate of basic pay, including a retained rate of pay under 5 U.S.C. 3594(c) or 5363 , for those hours during which the employee receives basic pay. This includes all periods of paid leave, detail, or travel status outside the COLA or post differential area.(b) Agencies pay employees eligible for both a COLA and a post differential the full amount of the COLA, plus so much of the post differential as will not cause the combined total of the COLA and post differential to exceed 25 percent of the hourly rate of basic pay.