The best time to visit Tanzania is during the Dry season, from late June to October, when wildlife viewing is generally at its best. The wildebeest migration in Serengeti usually starts on June as high season and time to see wildebeest calving is late January to February. The southern and western circuit parks are best visited during the Dry season (June to October), unlike the more popular northern circuit parks that can be visited whole year-round.
June to October (All parks), June-July and January-February (Serengeti for the wildebeest migration and calving)
July to March (northern circuit parks; they get crowded), July to October (southern and western circuit parks; they don't really get crowded any time of the year)
% Low Season
April and May (northern circuit parks still get quite a few visitors unlike the southern and western circuit parks, when many lodges close down)
June to October (Little to no rainfall)
March and April (Peak of Wet season)
The Serengeti and the Ngorongoro Crater offer good wildlife viewing throughout the year. June and July are the best months for seeing the migration, and February is the best month for the wildebeest calving. The dry months offer good wildlife viewing throughout Tanzania. Tarangire and the southern and western circuit parks (including Katavi, Selous and Ruaha) are best visited in the Dry season, from June to October.