5 USC 6303 - Annual leave; accrual

(a) An employee is entitled to annual leave with pay which accrues as follows
(1) one-half day for each full biweekly pay period for an employee with less than 3 years of service;
(2) three-fourths day for each full biweekly pay period, except that the accrual for the last full biweekly pay period in the year is one and one-fourth days, for an employee with 3 but less than 15 years of service; and
(3) one day for each full biweekly pay period for an employee with 15 or more years of service. In determining years of service, an employee is entitled to credit for all service of a type that would be creditable under section 8332, regardless of whether or not the employee is covered by subchapter III of chapter 83, and for all service which is creditable by virtue of subsection (e). However, an employee who is a retired member of a uniformed service as defined by section 3501 of this title is entitled to credit for active military service only if

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(A) his retirement was based on disability
(i) resulting from injury or disease received in line of duty as a direct result of armed conflict; or
(ii) caused by an instrumentality of war and incurred in line of duty during a period of war as defined by sections 101 and 1101 of title 38;
(B) that service was performed in the armed forces during a war, or in a campaign or expedition for which a campaign badge has been authorized; or
(C) on November 30, 1964, he was employed in a position to which this subchapter applies and thereafter he continued to be so employed without a break in service of more than 30 days. The determination of years of service may be made on the basis of an affidavit of the employee. Leave provided by this subchapter accrues to an employee who is not paid on the basis of biweekly pay periods on the same basis as it would accrue if the employee were paid on the basis of biweekly pay periods.
(b) Notwithstanding subsection (a) of this section, an employee whose current employment is limited to less than 90 days is entitled to annual leave under this subchapter only after being currently employed for a continuous period of 90 days under successive appointments without a break in service. After completing the 90-day period, the employee is entitled to be credited with the leave that would have accrued to him under subsection (a) of this section except for this subsection.
(c) A change in the rate of accrual of annual leave by an employee under this section takes effect at the beginning of the pay period after the pay period, or corresponding period for an employee who is not paid on the basis of biweekly pay periods, in which the employee completed the prescribed period of service.
(d) Leave granted under this subchapter is exclusive of time actually and necessarily occupied in going to or from a post of duty and time necessarily occupied awaiting transportation, in the case of an employee
(1) to whom section 6304 (b) of this title applies;
(2) whose post of duty is outside the United States; and

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(3) who returns on leave to the United States, or to his place of residence, which is outside the area of employment, in its territories or possessions including the Commonwealth of Puerto Rico.

This subsection does not apply to more than one period of leave in a prescribed tour of duty at a post outside the United States.

(1) Not later than 180 days after the date of the enactment of this subsection, the Office of Personnel Management shall prescribe regulations under which, for purposes of determining years of service under subsection (a), credit shall, in the case of a newly appointed employee, be given for any prior service of such employee that would not otherwise be creditable for such purposes, if
(A) such service
(i) was performed in a position the duties of which directly relate to the duties of the position to which such employee is so appointed; and
(ii) meets such other requirements as the Office may prescribe; and
(B) in the judgment of the head of the appointing agency, the application of this subsection is necessary in order to achieve an important agency mission or performance goal.
(2) Service described in paragraph (1)
(A) shall be creditable, for the purposes described in paragraph (1), as of the effective date of the employees appointment; and
(B) shall not thereafter cease to be so creditable, unless the employee fails to complete a full year of continuous service with the agency.
(3) An employee shall not be eligible for the application of paragraph (1) on the basis of any appointment if, within 90 days before the effective date of such appointment, such employee has held any position in the civil service.
(f) Notwithstanding any other provision of this section, the rate of accrual of annual leave under subsection (a) shall be 1 day for each full biweekly pay period in the case of any employee who holds a position which is subject to
(1) section 5376 or 5383; or
(2) a pay system equivalent to either of the foregoing, as determined by the Office of Personnel Management.