N.Y.C. Admin. Code § 13-307: § 13-307 Extra service pension credits.

Except as provided in subdivisions a and b of section 13-304 of this chapter, a member who has served the minimum period of time elected by him or her for retirement may continue in the service. In such event and upon his or her retirement for any cause whatsoever, there shall be added to his or her annual pension to which he or she shall upon his or her retirement be entitled an additional amount computed at the rate of one-sixtieth of his or her final salary for each year of such additional service. Any such member who has elected to contribute on the basis of retirement after twenty years of service and who thereafter continues in the service shall have his or her deductions made at the rate of five per cent per annum after completing twenty-five years of service.