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Typically, on birthdays, Buddhists practice social generosity, i.e. gift giving, as tokens of friendship and family association; this is done to re-establish connections. Buddhists believe generosity brings joy to the heart. In their culture, many Buddhists don't celebrate their birthdays in the same sense as Christians or other religions do.
However, some Buddhists do celebrate the day of their birth in a more traditional way, similar to the way we are accustomed, especially in America. Buddhists will try to do good deeds on their special day and believe it is even more special to do this on their birthday, in order to receive blessings. Traditionally, many Buddhists visit temples to pray or pray/meditate in a special area of their home on their birthdays.