The birthday effect is a real statistical phenomenon in which you are at increased risk of dying on, or near, your birthday.  In a Swiss study of mortality data, 13.8% more people older than 60 died on their own birthday than any other day.  

According to The Guardian, a 2016 Japanese study of mortality from major external causes confirmed that people were “more likely to die on their birthday than any other calendar day” by means of suicide, traffic accidents, drowning, and choking. For suicide cases in particular, people are 50% more likely to die on their birthday compared to other dates. Excess deaths were observed across the board regardless of gender, marital status, and age-at-death subgroups. The researchers suggested that for the suicides, the results provide strong support for the “birthday blues” hypothesis.

A major U.S. study using Social Security records of 25 million dead people found that the average excess death rate on their birthdays at 6.7%.

In a very large study of adult mortality that involved 2,745,149 people, U.S. researchers found that women are more likely to die in the week following their birthday than in any other week of the year. In addition, the frequency of female deaths falls below normal just before their birthdays. This could mean that women are able to prolong their lives until they reach a symbolic, meaningful occasion.  In contrast, male mortality peaks shortly before the birthday, suggesting that the birthday functions as a “deadline” for males.

The most common theory behind the birthday and death association is that a little too much celebrating may be going on that involves alcohol, says The Guardian. There is also the possibility that terminally ill people view birthdays as survival milestones and tend to pass on the day on either side of it.