2017
Monday, 7 August 2017
In 2017 the tithi runs from 10:28 pm on 6 Aug to 11:40 pm on 7 Aug; it is running at sunrise (the usual rule, called udaya tithi) on Monday, 7 August 2017, so that is the day of Raksha Bandhan.
2018
Sunday, 26 August 2018
In 2018 the tithi runs from 3:16 pm on 25 Aug to 5:26 pm on 26 Aug; it is running at sunrise (the usual rule, called udaya tithi) on Sunday, 26 August 2018, so that is the day of Raksha Bandhan.
How the date is fixed
Raksha Bandhan falls on the full-moon day (Purnima) of the lunar month Shravana. The date is the day on which that tithi is running at sunrise (the usual rule, called udaya tithi).
About
Raksha Bandhan falls on Shravana Purnima, in August. The thread is tied in the aparahna (afternoon) period, or failing that in pradosh, while Purnima is running and the Bhadra karana is not; since Bhadra always occupies the first half of Purnima, almanacs print the hour at which it ends. When Bhadra runs through the whole afternoon, the texts allow the next morning's Purnima if it is still present at sunrise. The same full moon is Narali Purnima on the Konkan coast and Shravani, the day of changing the sacred thread, for many communities.
How it is observed
Sisters tie a rakhi on their brothers' wrists in the afternoon; Brahmin communities renew the sacred thread.