The date of Magal De Touba varies because it is based on the Islamic Hijri Calendar. The day is on day number 18 in the islamic month safar.
The Islamic Hijri Calendar is a lunar calendar, which means that the calendar depends on the lunar phases. This means that, in the next ten years, Magal De Touba varies between May 17 and August 22. In the table below you can see the date for Magal De Touba in the coming years in the western calendar (Gregorian calendar).