Although Mount Kilimanjaro is known as a "walk-up" mountain, you should not underestimate it and its risks. The overall statistics show that less than half of all climbers reach the summit.
Below are the overall statistics of successful summits as reported by Kilimanjaro National Park:
All climbers, all routes 45%
All climbers, all 5 day routes 27%
All climbers, all 6 day routes 44%
All climbers, all 7 days routes 64%
All climbers, all 8 day routes 85%
Some companies boast that their client summit success rates are greater than 90%. We have seen competitor advertisements representing they have 95%, 98%, even 100% success rates. This is statistically impossible! Do not believe these claims!
Unless these outfitters are prescreening climbers, taking a very small number of climbers (less than 30) per year, or leading climbs only on 8-9 day routes, achieving those extraordinarily high success rates would be ridiculously improbable and impossible to maintain for even a short period of time. Every outfitter knows this, but unfortunately it seems some don't mind attracting customers with misleading or blantantly false statements.
The greater the number of days on the mountain, the better your chances of reaching the top.
There is a strong correlation between days and success. A successful summit bid is usually a question of how well a climber can acclimatize to the high altitude, rather than the climber's ability to ascend. How one reacts to high altitude is uncertain. Some people's bodies adjust well to the decreased oxygen levels; others do not. Being physically fit and in good health is no guarantee of your ability to acclimatize.
So how long does it take to climb Kilimanajro? There are minimum days for each of the six Kilimanjaro climbing routes. However, that is not to be confused with recommended days for the route. Ultimate Kilimanjaro recommends adding an extra day or two to your trip to help you acclimatize to the altitude. We encourage customers to take 7-8 day routes.

Our primary concern is that you have a safe, enjoyable, memorable Kilimanjaro climb.
It is possible to climb the mountain in five or six days, but why take the chance? Some clients want to minimize their days in order to save costs, which is understandable. But we feel that the additional cost is well worth it. Not only is it safer, but you increase the probability of your success, have more time to enjoy the experience, can take acclimatization hikes to other parts of the mountain you'd otherwise miss, and will probably feel better as well, given that there is less stress on your body.
Ask yourself this. How would you feel if you scheduled a route with the minimum required days, only to have to turn around within the first couple days because the ascension rate was too quick? Wouldn't you rather have added a couple days to your trip to give yourself a better chance, to be more fair to your body? Were the 'savings' you got for not taking additional days worth the cost of cutting your climb short, not making it to summit, or even worse, putting your health at risk?