September-November is the best season to visit Kathmandu. Since this is the period when the dry season starts and also the air is clean and the weather is pleasant so for touring this is the best time. As this time is the time for festivities and so a lot of cheerfulness is there in the air. December and January should be avoided as the cold sets in and lasts till the end of January.

February-April is the second best time to visit Nepal as this period is the tail end of the dry season. During this period the air is fresh with the flowers bursting into bloom and again this is a lovely time to be in Kathmandu.

The monsoons begin from May and at that time the heavy rains hit the city - this irregular rain goes on till August. During monsoon season it is inconvenient to take part in outdoor activities, so this period should be avoided but as this is an off season period so everything related to tourism can be available at a very low cost and so most people prefer to visit Nepal in monsoon season too. So, in nutshell we can say that if we think about as to when to visit Nepal then the answer will be throughout the year.