The best time to come to Bhutan would be in March, April, May, September, October and November. There are many festivals during these periods, and visitors come to take advantage both of the pleasant climate and the wonderful festivals. However, Bhutan has limited tourism infrastructure and during peak seasons facilities are packed, so one has to book the tour well in advance or for those wanting to avoid the busy tourist periods the winter months of January, February June and December are recommended. You still have a lot to see in the off season too.