October to February is the best time — cool days (15–22°C), clear skies, and views that stretch to the horizon. March and April are warmer but still manageable; May gets hot and humid before the monsoon breaks in June.
The monsoon runs June to September and transforms the hill: lush green forests, cascading waterfalls, low cloud, and mist. It's dramatic but the paths get muddy, some viewpoints become inaccessible, and the train occasionally stops running. A few visitors come specifically for the monsoon scenery — you take your chances with the weather.
Avoid major Indian public holidays and Mumbai school holiday periods, when the hill gets overwhelmingly crowded and hotels charge peak rates. Midweek visits in the October–February window are the sweet spot.