Prime Minister Srettha Thavisin said the decision was made two months before the festival so that people and businesses would have plenty of time to plan ahead, reports the Bangkok Post.
He would like the Ministry of Tourism and Sports to promote second-tier provinces for the long holiday, which will now run from Apr 12-16 inclusive.
Apr 13-15 are the conventional Songkran holidays. Apr 16 is a holiday in lieu of Apr 13, which is a Saturday.
The Cabinet secretariat said that apart from tourism promotion the extended holiday would help ease traffic congestion because it allowed people more flexibility in planning their trips.