To answer your question straight out, the best time to hike Machu Picchu, in our opinion, is on the shoulder months of the dry season, Late April / Early May and Late September / Early October. At these times the trails tend to be significantly quieter than peak season, the Citadel less packed and the weather conditions relatively good.
If you are not too bothered about crowded trails, busy hotels and the tourist hordes that visit Machu Picchu by train from Cusco each day then the best time to hike Machu Picchu is during the dry and peak season which runs from May through to September.
If you decide to go during the peak season you will need to book early if you want to grab one of the 500 permits available on the Inca Trail each day (note: about half are taken by guides and porters). Alternatively you could trek on the less popular (yet equally authentic trails) of Salkantay, Lares or Vilcabamba, but be prepared for a more challenging hike – see trail and route options here.
The wet season begins in November and gets into full swing over the months of December, January and February. The Inca Trail is closed every year in February for restoration. We do not recommend trekking Machu Picchu in these months, although if you plan to catch a train from Cusco you can get lucky with the weather and have a lovely day in Machu Picchu.
November and March are risky months for trekking (not for visiting Machu Picchu by train) but it is still possible to encounter limited rain. The upside of these months is that you will have the trail largely to yourself.
In this article we provide useful historical weather charts on temperature, rainfall and wind. You will notice that like most of the sub-tropics in the Andes, there are only two season – dry (May-September) and wet (November-April), and that temperature are moderate during the day and cold at night.