Since the number of trek permits is limited to 500 per day (about 200 tourists and 300 trekking staff) it is important to book well in advance. The trek permits are issued on a first-come-first-served basis up until all the permits have been sold out. In the low season (December & January) there are some days when there are still permits available 4 or 5 days in advance, but in the high season (May to September) it is recommended that you book at least 4 months in advance to guarantee a place. We would actually recommend making a reservation 5 or 6 months ahead. You can check out how many permits are left on our webpage Inca Trail trek permit availability. If the Inca Trail is already fully booked on the departure date that you require you can always consider one of the Alternative Inca Trail Treks