Please be aware that Kuala Lumpur has multiple airports and that these results are for all airports serving the city.
The best month to fly between Kuala Lumpur and Hanoi is May and the most expensive month to fly is September. (Average prices, based on 2067 datapoints.)
The best day to arrive at Kuala Lumpur is Sunday and it would be best to avoid Saturday, as prices are on average 38.69% higher than on Sunday. (Average prices, based on 2067 datapoints.)