High Season: October to February
The high season for Rajasthan officially begins in October, though the large Spanish tour groups begin arriving in August and September. The peak is November through mid-February when the weather is at its best, the days are perfect for sightseeing and evenings are pleasant—and can even be chilly in the desert areas. Temperatures rarely rise above the mid-80s, but the sun is still strong, so cover up if you're susceptible to sunburn. Many hotel rates are close to double those charged in low season, and monuments are crowded with group tours. This is also when the Ranthambhore National Park is open and the winter migratory birds come to Bharatpur (Keoladeo Ghana) Bird Sanctuary.
Low Season: May to July
These summer months can be unbearably hot, with temperatures, particularly in desert cities like Jaisalmer and Jodhpur, at times soaring close to 120 degrees. It's almost impossible to endure a full day of sightseeing. As a result most hotels are vacant and offer great deals—often less than half their usual rates—and the monuments are either deserted or sparsely dotted with a few random tourists.
Shoulder Season: August to September and March to April
As long as you don't mind the monsoon, this is not a bad time to visit. The weather is neither at its best or its worst, and crowds can easily be avoided. However, hotel deals are not as highly discounted as in the low season, and the wildlife parks are closed because they sometimes flood.