We don't know the exact date of his birth. We do have a record of his baptism, which was on 26 April 1564. It was usual for babies to be baptised within a few days of birth as there was a high infant mortality rate, and it was thought important for new babies to receive the blessing of the church quickly in case they didn't survive. So it's certainly possible that Shakespeare was born on St George's Day, which is on 23 April, and highly likely that he was born at around that time. But the main reason why a lot of people think of him as being born on 23 April is because Shakespeare has become one of England's greatest cultural figures - in fact probably the greatest - so the idea of him sharing a birthday with the day of England's patron saint is quite appealing. It is known for sure though, that he died on St George's Day (in 1616, at 52).