There are two main climbing seasons which are generally considered the most favorable time to climb Kilimanjaro; these are January to March and June to October. 

January-March is generally dry but a little bit colder during the evening and early morning compares to June-October at this time there is higher possibility of encountering snow on the summit.

June-October climbing season is the longest dry season and most favorable climbing time and it coincides with the summer holidays in Europe and North America and hence certain routes are often quite busy.
March, April and November are the wettest months on Kilimanjaro and theoretically not ideal for climbing for hiker with less experience in mountain environment and altitude sickness although it’s climbing season with larger discount in pricing

NB – However, since the mountain creates its own weather and conditions can change rapidly, regardless of the season, you should be properly prepared for all conditions, no matter which time of the year you choose to climb.

The chart below addresses the pros and cons of climbing within and outside the two distinct climbing seasons.

January to March	April and May	June to early November	November to mid-December
Dry and quiet	Long rainy season	Long dry season	Short rainy season
The weather in the first few months after the short rainy season is generally warm and dry. Being “off season” and therefore relatively quiet, it is our preferred time to climb Kilimanjaro.	The long rainy season in Tanzania normally occurs in April and May, although it has become more unpredictable in recent years. If you don’t mind the rain you can have the mountain pretty much to yourself.	June to early November are the driest months for your Kilimanjaro climb. This means the mountain is busy, especially from August through October. June, July and early November are a good compromise.	Generally rain is less persistent than during the main long rain season, it only last for 3 to 4 weeks, normally starting for the last week of October to mid December. This is also a good  time to be on the mountain