and (b) the average annual rate of basic pay of the employee's highest-paid consecutive 36 months (three years) of service (commonly referred to as the "high-3" period). The "high-3" pay includes all items for which retirement deductions are withheld; this includes basic pay, locality pay adjustments and shift differentials, but not overtime (except in special circumstances mainly involving first responders), bonuses/awards, severance pay or buyouts, payments for unused annual leave and credit hours, or "hazard pay" (additional pay for certain "hazardous" duty assignments, such as working in a combat zone). All salaries earned during the "high-3" period are time-weighted, and include COLA's, within-grade (step) increases, and promotions. The "high-3" period normally is the final three years of service but does not have to be (e.g. an employee taking a voluntary downgrade to avoid a reduction-in-force (RIF) could have a high-3 period in an earlier time frame). The FERS annuity is structured to provide employees an incentive to continue working for at least 20 years in Federal service and until age 62 (which is also the earliest age at which a FERS employee can collect Social Security benefits), since employees retiring at or after age 62 with 20 years of service or more have the annuity calculated at 1.1 percent of the high-3 average times the number of years worked (including fractional years using months but not days), while employees not meeting those criteria have the annuity calculated at 1 percent of such. Separate calculations exist for certain workers (mainly Members of Congress or congressional staff, law enforcement officers, firefighters and air traffic control specialists) and for employees who transferred from CSRS to FERS. An employee retiring under age 62 will receive a "special retirement supplement" which duplicates what an employee would earn under Social Security at age 62, but at age 62 the supplement ends. Disability retirement annuity payments are offset totally by any Social Security disability payments for the first 12 months, and then partially afterwards until age 62; at that time the annuity is treated as if the employee had worked for the entire period of disability (but at the same grade and step, with no within-grade increases or career ladder promotions taken into account), and the "high-3" and resulting annuity is recalculated taking into account any COLA's that would have been earned between the original retirement and age 62. Unused sick leave is converted, at 100% of