The short answer
If you only have one window in the year and you want clean weather, no rain, snow on the high passes, and every road open from Dharamshala to Spiti, come in the second half of September or the first three weeks of October. That is the cleanest window in the Himachal calendar — and the one most repeat travellers ask us to book again.
If you have flexibility, the answer changes by what you want to see.
March to mid-June: spring and early summer
Wildflowers in Palampur tea gardens, rhododendron blooms along the Triund trail above McLeodganj, snow still on the upper passes. Rohtang Pass opens in mid-May most years; the Atal Tunnel is open year-round. April afternoons can hit 28°C in Kangra valley but mornings stay cool. Manali fills up with Indian honeymooners after April 15 — book hotels two weeks ahead.
Spiti opens through Kinnaur route by late April; the Manali–Kaza route (Kunzum Pass) usually opens between May 20 and June 15 depending on snow. We re-route Spiti tours via Kinnaur in early-season bookings — adds two days but avoids gambling on Kunzum.
July to mid-September: monsoon
Green at its most lush — but with real risk. The Kullu–Manali highway sees landslides almost every monsoon week. Spiti stays mostly dry (rain-shadow) and is actually the cleverest time to visit if you can fly to Bhuntar and reverse-route from Kaza. Dharamshala monasteries are atmospheric in the mist; bring a light rain jacket and waterproof shoes.
We do not run Manali–Spiti–Kullu loops during peak monsoon (third week of July through August). We run Dharamshala–McLeodganj–Bir, Amritsar combinations, and Spiti via Kinnaur instead.
Mid-September to November: the second peak
Crisp, dry, no rain, apple harvest in Kullu, golden poplars in Spiti. This is when foreign trekking groups come for Hampta Pass and the Pin Parvati. By mid-November Spiti closes via Kunzum; Manali starts to feel cold; the high lakes (Chandratal) become inaccessible. Dharamshala stays comfortable through November.
December to February: snow season
If snow is the point of the trip — Manali, Solang, Khajjiar, Dalhousie, parts of Shimla — December and January are spectacular. Roads to Rohtang are closed for the season but the Atal Tunnel keeps Sissu and Lahaul open in good weather. Dharamshala and McLeodganj stay mild (5–15°C), monasteries are quiet, and the Tibetan New Year (Losar) usually falls in February or March.
Spiti, Lahaul beyond Sissu, and high Chamba are closed in winter.
Festivals worth planning around
Navratri (twice a year, March-April and September-October) at Brajeshwari, Chintpurni and Jwala Ji temples. Kullu Dussehra (October) — a week-long procession of village deities, one of the most photographed festivals in India. Losar (Tibetan New Year, February-March) at McLeodganj. The Dalai Lama's birthday teachings on July 6, when scheduled, fill McLeodganj — book three months ahead.