Bisu, also known as Tulu New Year Day, is the first day of Tuluva calendar followed in Tulunadu region in Karnataka. In 2018, Bisu date is April 14.
The entire stretch of Udupi, Dakshina Kannada and parts of Kasargod is known as Tulunadu. The people of Tulunadu follow Souramana Panchanga (Solar calendar) hence this festival is also referred to as Souramana Ugadi.
Bisu is the period of transition of seasons where Suggi month ends and the Paggu month begins.
It is to note that other parts of Karnataka celebrate Kannada New Year on Ugadi day (Chandramana Ugadi – Chaitra Pratipada).