On January 2016, the Peruvian government added 250 trek permits are issued per day for the short Inca Trail Inca Trail. The bad news is that the website that shows availability is not open to the public.
Before 2016 you may have heard about the limit of 500 people per day allowed on the Inca Trail. Included Inca Trail 4 days , Salkantay Inca Trail 7 days and Inca Trail 2 days. Between March 2016, the Ministery of Cultura classified two Inca Trail systems: