There is not really a right or wrong time to visit Vietnam, as during most months of the year you will experience both sunshine and rain in varying quantities. 
Whilst the country is typically warm and humid, the weather can vary significantly from one region to another. There can be snow in the mountainous far north, whilst the beaches in the south enjoy 30-degree heat and sunshine. 

The climate can broadly be divided into two seasons - wet and dry. The cooler dry season typically runs from October to late March. In the north, including the capital Hanoi, daytime temperatures average in the low 20s Celsius, with the coldest months being January to March. Across the mountainous far north, it can get very cold and frosty in December and January, especially at night.

Summer lasts from April to September. It’s humid at this time of year, with temperatures in the low to mid-30s Celsius. Throughout much of the wet season, rainfall is generally heavy but short-lived, often occurring as mid-afternoon heavy downpours.

Further south the heat is more evenly distributed through the year. And, come rain or shine, the far south, including the popular islands of Phu Quoc and Con Dao, can expect 30-degree heat year-round. Perfect for the beach - but don’t forget the sunscreen!