The main climbing seasons for Kilimanjaro are from June to October and from mid-December to early March. These are actually the “dry seasons” in the region because of the low rainfall during this time in the region. At these times you can expect good weather and little rainfall. This is when Kilimanjaro and the safaris in the national parks are the busiest, especially during the general holiday periods in Europe and North America.

The probability of rain is drastically higher during the rainy season in the months of April, May and November. Drawbacks of attempting Kilimanjaro in the rainy season are:

• Obscured views of the peaks due to cloud and rain
• Walking under rain on muddy trails
• Higher snow levels on the upper reaches of Kilimanjaro

Month wise reference to hike Kilimanjaro:

• Mid-December to early March – The colder of the two dry seasons, this is the best time to experience clear skies on your climb. The colder temperature also means that there will be snow on the upper reaches of the mountain. There may be brief showers during this period. You will also experience lesser crowds on the trail which makes the climb up Mt. Kilimanjaro more serene. People say this is an exceptionally beautiful time of the year to climb Kili.
• mid-March to May – Heavy rains are to be expected during this time. It is still a doable climb, but the climb is tougher and vehicles can sometimes not make it to the starting point ( route dependent ). If this happens, you may have to start your trek earlier than expected. Some routes may be better than others during this period.
• June to October – The second dry season and the main tourist season for climbing Mt Kilimanjaro. The weather is quite conducive for the trek, irrespective of the route. Though you will have occasional rain and low hanging clouds, as the monsoon recedes in June, higher altitudes will give clearer skies. You will find that the trails / camps are more crowded during this time. This is because a major part of the crowd comprises of people from Europe and America, where the academic session is on break. 
• November to mid-December – This season brings the rains back to the mountain slopes. These rains are lesser in intensity as compared to the ones in April/May.