Deoghar is a year-round destination, but the busiest period is Shravan (usually July-August) during Shravani Mela and Kanwar Yatra, when lakhs of devotees arrive - expect crowds, but also the most vibrant atmosphere. For a calmer visit with shorter temple queues, October to March offers pleasant weather and comfortable sightseeing. Summers (April-June) are hot and best avoided unless visiting specifically for the pilgrimage season.