If you are thinking of having a baby, best wait until Christmas.
A child conceived in December has a better chance in life than one conceived this month, with a lifetime of unhappiness, poorer prospects and lower earnings awaiting them.
A summer or autumn birth is a key determinant of a child's wellbeing and its impact may be felt long into adulthood, researchers have found.
Previous studies have shown that children born at the start of the academic year in September do better at exams than those born in August.
As the oldest in their year group, when September babies start school they have a significant advantage over others in their peer group -- while those born in August are younger and lag behind.
Now research by the Institute for Fiscal Studies (IFS) has shown that these effects go beyond test results. Children born in August do worse in national achievement tests, are less likely to attend a top university, and are less likely to gain experience of leadership as captain of a team or chair of a club.
They also have less confidence in their academic performance and less belief in their ability to control their own destiny than those born in September. The effect was evident across social classes, suggesting that better-off families are no more able to overcome the penalties which August-born children suffer than poorer ones.
Claire Crawford, programme director at IFS and an author of the report, said: "All these [factors] are associated with a greater chance of being in work and having higher wages later in life.
"This suggests that August-born children may end up doing worse than September-born children throughout their working lives, simply because of the month in which they were born."
The differences were evident as early as aged seven, when August-born children were two to three times more likely to be judged below average by their teachers in reading, writing and maths, and at least twice as likely to report being bullied or to say they were unhappy at school.
Other studies have shown a link between being born near the start of the school year and becoming a professional sportsperson.
A child born at the start of the academic year has almost 12 months growth ahead of their classmates.
The researchers said there was evidence that parents strive to compensate for the disadvantage suffered by their summer-born children, by spending more time at home helping them to learn.
But their efforts, it seems, cannot close the gap.