Timing changes everything.

The long rains run from roughly late March to May. This is the wettest part of the year. Rain usually arrives as heavy afternoon storms rather than all-day drizzle, so game viewing continues, but unsurfaced tracks — particularly in the black-cotton soils of the Serengeti and parts of the Mara — become genuinely difficult, and some seasonal camps close.

The short rains fall around November into early December. They are lighter and more scattered, and rarely disrupt a trip. They green the country quickly, which is why November is one of the most attractive months for photography and birding.

The dry seasons — roughly June to October, and again January to early March — are the classic safari months. Grass is short, water is scarce, and animals gather at the remaining rivers and waterholes, which makes them easier to find and to photograph.

Altitude matters as much as season. Most of the safari circuit sits between 1,000 and 2,300 metres, so even in the hottest months dawn game drives are cold enough to want a fleece. The Ngorongoro crater rim at 2,300 metres is genuinely chilly at night year-round.

The guidance below describes long-run patterns. Weather and wildlife movements are natural phenomena: seasons shift by weeks from year to year, and nobody — including us — can guarantee where the herds will be or whether it will rain on a given date.

The migration is a year-round circuit, not a season. Around 1.5 million wildebeest and several hundred thousand zebra move continuously through the Serengeti–Mara ecosystem in search of grazing, and the herds are somewhere in that system every month of the year. The question is never whether you can see the migration — it is which part of it you want to see.

Calving (late January – March): the southern Serengeti and Ndutu. Enormous concentrations on open short-grass plains, newborn calves, and the most intense predator activity of the year.

The move north (May – June): columns of animals stretching for kilometres through the central and western Serengeti, with the Grumeti River crossings in June.

Mara River crossings (July – October): the famous images. Herds cross north into the Maasai Mara and back again repeatedly. Crossings happen on the animals' schedule, not yours, and cannot be guaranteed by any operator.

The return south (November – December): the herds drift back through the eastern Serengeti as the short rains green the southern plains.

Our migration journeys are built around these movements, and our full migration guide goes into more detail.

Both countries have excellent resident wildlife every month, so timing matters most if the migration is your priority. Between July and October the herds are usually in or around Kenya's Maasai Mara. Between December and March they are on Tanzania's southern Serengeti plains.

Outside those windows, choose on character rather than calendar. Kenya packs more variety into shorter distances — Mara grassland, Amboseli's elephants and Kilimanjaro views, Lake Nakuru's rhino, Rift Valley lakes — which suits shorter trips. Tanzania is a bigger, emptier landscape with the Ngorongoro Crater as a genuine one-off, and it rewards longer itineraries.

Eleven of our journeys cross the border and cover both. If you are weighing them up, Kenya or Tanzania? compares them properly.

Kilimanjaro and Mount Kenya share the same two climbing windows: January to mid-March and June to October. Both are drier, with firmer trails and better odds of a clear summit morning. January and February are usually warmer; the mid-year window is colder but very stable.

April, May and November are the wet months and are generally avoided. Trails become slippery, the scree above the last camp is harder work, and summit views are often cloud-covered.

Whatever the month, altitude decides the outcome more than weather. Longer routes acclimatise better: our eight-day Machame programme has a materially better summit record than the five-day Marangu. Browse climbing & trekking for every route we run.

Uganda's forests are wet year-round — Bwindi is rainforest and can rain in any month. The drier windows, June to August and December to February, make the steep forest trails firmer underfoot and the trek considerably more comfortable.

The real constraint is not weather but permits. Gorilla permits are capped, allocated well in advance and priced separately from any safari. If gorilla trekking is part of your plan, the permit date should anchor the whole itinerary rather than be fitted around it. See our Uganda guide.

The coast runs on a slightly different calendar to the safari circuit. June to October is dry, warm and breezy — and lines up neatly with peak safari season, which is why it is the most common combination. December to February is hotter and humid with excellent diving visibility.

April and May are the wettest months on the coast and some hotels close for part of that period. Tides matter more than most visitors expect on Zanzibar's east coast, where the water retreats a long way at low tide — the north coast around Nungwi and Kendwa stays swimmable throughout. More in the Zanzibar guide.

Families are usually tied to school holidays, which in practice means July, August and December. July and August are ideal — dry, cool in the mornings and the strongest wildlife months — but they are also the busiest and most expensive, so book early. December works well in the first three weeks. In peak months a private vehicle is worth more with children than at any other time, because you can leave a sighting when they have had enough.

Photographers often prefer the green season to the peak. January to March gives newborn animals, saturated colour and dramatic storm light; June to October gives dust, low golden sun and concentrated animals against clean short grass. November brings migratory birds and the most interesting skies of the year. All of them beat a cloudless midday in August.