Big birthdays, big decisions

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Anthropology / Health / Myths / Psychology

Have you got a big birthday coming up, one that ends in a zero? And have you made any major life decisions recently? Although we measure time using a continuous scale, research has shown that in the year before a milestone birthday, people are more likely to reflect on their lives and make significant changes. Given destructive behaviours can result, it’s worth trying to understand why we are so affected by what are essentially arbitrary points in time.

Research shows we're more likely to make major, life-changing decisions just before milestone birthdays. But why? Image credit: Dave Haygarth via Flickr.

Research shows we’re more likely to make major, life-changing decisions just before milestone birthdays. But why? Image credit: Dave Haygarth via Flickr

Happy birthday to you

Whether you are 29 or 32, or 38 or 41 right now, your age probably doesn’t have a strong influence on your life. In fact, unless you are about to hit 18 or another milestone that will make it legal for you to vote, drive or drink alcohol, I’m guessing your exact age is fairly meaningless.

But research shows humans are very tuned into real or perceived fresh starts when it comes to changing our habits and tackling our personal goals. For example, we know people are more likely to think about their health on Mondays. And people Google the term ‘diet’ and go to the gym much more often at the start of each new calendar cycle: the beginning of a week, month or year, as compared to at other times. Ever made a New Year’s Resolution?

And it turns out, birthdays act as strong landmarks for us, interrupting the ‘seemingly unending stream of trivial and ordinary occurrences that happen to us every day’. No surprises then that a birthday has the power to inspire changes in our behaviour.

Research published late last year explored whether approaching a new decade in age has any effect on our behaviour. The researchers looked at a few specific behaviours of people aged 25 to 64. They were particularly interested in people they nicknamed the ‘9-enders’ – people aged 29, 39, 49 and 59.

What’s the meaning of life?

First the researchers considered results from the World Values Study. As part of this study, more than 42,000 people from 100-odd countries were asked how often they think about the meaning of life. Most people reported thinking about the meaning and purpose of their lives often, but 9-enders were found to consider these things significantly more often than people whose age ended in any other digit.

We might expect that contemplating whether your life has meaning could result in either a positive or negative response depending on your conclusion. And that’s exactly what the researchers found.

Of marathons and affairs

On the positive side, being a 9-ender makes it more likely you will run your first marathon, a definite positive challenge. The researchers looked at the ages of 500 first-time marathon runners and 74 of them were 9-enders. That number is 48% more than we would expect if age had no relation to when people decide to run their first marathon.

The researchers also looked at whether race times suggest 9-enders train harder than at other stages of their lives. And yes, runners aged 29 or 39 tended to finish about 2% faster at this age compared to the years before and after that birthday. This suggests they trained harder for the race in the year before they turned 30 or 40.

But the study also assessed the ages of more than 8 million male users on an online dating site specifically designed for people seeking affairs. There were more than 950,000 men aged 29, 39, 49, or 59 which was nearly 18% more than would be expected by chance. (Note the pattern was also true for women, but the trend wasn’t as strong).

Major birthday, major decisions

People are more apt to evaluate their lives as a chronological decade ends and, as a result, more likely to make life-altering decisions Adam Alter and Hal Hershfield, authors of the  study “People search for meaning when they approach a new decade in chronological age”

Why do these milestone birthdays have such an effect on our behaviour? There are a number of theories. For example, on the positive side, it may be that the start of a new decade allows us to feel somehow separate and disconnected from our past imperfections, providing inspiration to improve ourselves. It could also be that a significant birthday takes away our focus from the day-to-day minutiae of life and encourages us to think about the big picture and meaning of our lives.

Whatever the reason, the message is clear. If you’re a 9-ender, be prepared for some soul-searching and decision-making. As for me, I hit the big 4-0 last year so I reckon I’m off the hook. For now.

Links and stuff

Radio on demand

 This post accompanies a radio segment on Triple R’s Breakfasters program on Wednesday 25 March 2015. 


  1. I think looking back at 39 I soul searched for the greater meaning and had great plans and ideas for 40. Then at 40, denial kicked in – maybe if I don’t think about turning 40, then maybe it didn’t happen? Two years later, reality kicked in, no more excuses and I got on with it. 🙂

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