Sinhalese New Year, generally known as Aluth Avurudda in Sri Lanka, is the new year of the Sinhalese people in Sri Lanka. It is a major anniversary celebrated by not only the Sinhalese people but by most Sri Lankans. The timing of the Sinhala New Year coincides with the new year celebrations of many traditional calendars of South and Southeast Asia. The festival has close semblance to the Tamil New year Thai New year, Bengali New Year,Cambodian New Year,Lao New Year,Thingyan, in Myanmar and Oriya New Year festival in India. It is a public holiday in Sri Lanka. It is generally celebrated on 13 or 14 April.
According to Sinhalese astrology, New Year begins when the sun moves from Meena Rashiya (the house of Aries) to Mesha Rashiya. It also marks the end of the harvest and spring.
Source from Wikipedia.org