Spring and fall are the most promising times to visit New Delhi, with the broader tourist season stretching from October to late March. By April, the heat approaches 100 degrees. It sticks in the triple digits until July, when the monsoon rain comes, cooling things down but turning the streets into a boggy mess. As the seasonal rains pass, the city stays relatively cool and—for a brief time, despite the pollution problems that plague the city—clean. With the first full moon between mid-October and mid-November comes the Hindu holiday of Diwali, a celebration of Lord Rama’s triumph over evil, featuring fireworks and festive lights for five days.
If you plan on being in Delhi from late December through February, keep in mind that the temps can be relatively cool, especially at night, dipping down to the lower 40s. This is a good time to catch outdoor classical music concerts (popular Sufi devotional concerts take place all year in Nizamuddin). On January 26, India observes Republic Day, celebrating the adoption of its constitution—a big deal, with military parades and millions of spectators. Usually beginning in February, the exquisite Mughal Gardens behind the presidential estate open for public viewing for about a month.
March and April are the final months before things get too hot for most visitors. Travelers fill the city, making their way from south India to the Himalayas. The celebration of Holi, an Easter-like holiday when participants often find themselves colored with dye as part of “color wars,” takes place in mid-March.