There is no single perfect Kilimanjaro date
Most trekkers prefer drier weather windows because trails, camp life and summit conditions can be easier to manage. Weather on a high mountain can still change quickly in any month.
Common drier windows
Late December into early March and roughly mid-year into early October are commonly selected climbing periods. They can also be busier on popular routes.
Rainier periods
Rain can make lower trails wetter and cloud can reduce views. A quieter mountain may appeal to experienced travellers, but the final route and equipment plan should account for the conditions.
Choose the route and duration together
The best date is only one part of the decision. Route length, acclimatisation, group experience and the rest of your Tanzania trip should be planned together.