What class of medical certificate must I hold and how long is it valid?

• A first-class airman medical certificate is required to exercise the privileges of an airline transport pilot certificate. A first-class airman medical certificate is valid for 12 months plus the remainder of the days in the month of examination for pilots under age 40 or for 6 months plus the remainder of the days in the month of examination for those pilots age 40 and over.
• A second-class airman medical certificate is required for commercial, non-airline duties (e.g., for crop dusters, corporate pilots) and is valid for 1 year plus the remainder of the days in the month of examination. Those exercising the privileges of a flight engineer certificate, a flight navigator certificate, or acting as air traffic control tower operator must hold a second-class airman medical certificate.
• A third-class airman medical certificate is required to exercise the privileges of a private pilot certificate, recreational pilot certificate, a flight instructor certificate, or a student pilot certificate. A third-class airman medical certificate is valid for 5 years plus the remainder of the days in the month of examination for pilots under age 40 or for 2 years plus the remainder of the days in the month of examination for those pilots age 40 and over.