Expansions rotate every April. So 4 months ago Old Gods, Karazhan, and Gadgetzan rotated and next April Un’Goro, Frozen Throne, and Kobolds will rotate. Expansions that come out in April are in standard for 2 years, August expansions are in standard for 1 year and 8 month, and December expansions are in standard for 1 year and 4 months.
Expansions rotate every April. So 4 months ago Old Gods, Karazhan, and Gadgetzan rotated and next April Un’Goro, Frozen Throne, and Kobolds will rotate. Expansions that come out in April are in standard for 2 years, August expansions are in standard for 1 year and 8 month, and December expansions are in standard for 1 year and 4 months.