People born in summer have a sunnier outlook than those born in colder months, the results of a survey show.
The month they were born in could be crucial
More than 40,000 members of the public took part in the online survey.
Those who were born in May were the most likely to consider themselves lucky while those born in October had the most negative view of their lives.
Professor Richard Wiseman, who conducted the research, said people born in winter could improve their luck by being more optimistic.
People who took part in the survey gave their birthdates and rated the degree to which they saw themselves as lucky or unlucky.
The poll found there was a summer-winter divide between people born from March to August and those born from September to February.
Professor Wiseman, a psychologist at the University of Hertfordshire, launched the research at the Edinburgh International Science Festival and presented the results at the end of the meeting.
They showed 50% of people born in May considered themselves lucky, while this figure dropped to 43% in October.
Professor Wiseman pointed out that those born in May see the whole of summer in their first six months, while the first experience of those born in October is the winter months.
Fellow researcher Professor Jayanti Chotai, of Umea University in Sweden, has previously shown people born in winter are less likely to seek out novel experiences.
He said: "The environmental factors around the birth period, like exposure to sunshine and temperature, could all influence the body's biological systems, with effects extending into adulthood."
Professor Wiseman said the effect may be due to a difference in the way parents interact with their babies during summer and winter.
He added: "The good news for winter-borns is that people can improve their luck by being more optimistic and making the most of the opportunities that come their way."
Summer-borns include rugby player Jonny Wilkinson, author J K Rowling, footballer David Beckham, and model Jordan.
Winter-borns include singer Peter Andre, presenter Vanessa Feltz, Prince Charles, and liberal democrat leader Charles Kennedy.
Diana Pidwell, a clinical psychologist in Blackpool, said there had been research showing a connection between the time of year a person is born and what they choose to do for a living.
She said: "It might also be feasible that your level of optimism or your likelihood of being depressed may be affected by the time of year you were born."
The connection might be due to summer babies being around happier people and being taken outside into sunlight while winter babies are kept indoors.
Ms Pidwell added that, except in case of clinical depression: "How happy you are is very much to do with how happy you decide to be."
But thinking you are lucky is not all good news, according to Dr Michael Wohl, assistant professor in the Department of Psychology at Carleton University, Canada.
He has researched people's perception of their own luckiness.
Dr Wohl said: "Some people understand luck as a personal quality that can be used to maximize outcomes. Thus, lucky people might be prone to acting impulsively."
The more they believe they are lucky, the less they think they have to worry about negative outcomes.
He said this could lead to developing habits such as gambling.