“Spanish

How to hack your year

This story is part of a series we’re running on how to ‘hack’ your year. We’ll be looking at the best time of year to get engaged, buy a house, sit an exam, go to hospital and more. Keep checking back through December here for more stories.

When we’re trying to make a big decision, many of us think (and over-think) about the choice itself. If we’re really analytical, we might also think about our decision-making process: should we write up a list of pro’s and cons, or make a weighted spreadsheet? Research endlessly, or cut ourselves off from accumulating too much data?

But as well as thinking about how to make a choice, we may also want to think about when to make it.

Whether it’s changing careers or buying a house, January always feels like a prime time for a reset – or, at least, to decide on a reset. And many of us are returning from holiday, where free time and conversations with loved ones can make us think about our life choices.

But is January really the best time to make a big decision?

You might also like:
Should you trust your gut feelings?
Why contemplating death changes how you think
How good are you at thinking about uncertainty?

The answer depends on our mood.

Many of us find that we feel a little lower in winter. For some people, it can be extreme. Seasonal affective disorder (SAD), marked by having depressive episodes in the winter months, is especially common in northern latitudes. One review found that up to almost 10% of people in the north, including North America, are affected by the disorder, while a recent study in Switzerland following participants over more than 20 years found that 7.5% of the population experienced seasonal depression.

Symptoms also can last for longer than you might expect: one study found that in the US, those affected by SAD struggle with symptoms for an average 40% of the year.

But even those who don’t meet the diagnostic criteria for SAD often feel that their mood is lower in the winter. Back in the 1980s, a telephone survey of Maryland residents found 92% of people noticed seasonal mood changes to some degree – mainly that their mood became lower in winter.

Your mood doesn’t just affect how you feel. It can affect your decision-making abilities. But to make matters more complex, having a low mood doesn’t mean you’ll always be worse at making a choice.

Reward risk

A depressed mood tends to make us more risk-averse. Researchers think this may stem from a curtailed ability to experience pleasure, meaning a depressed person doesn’t have the same potent (and optimistic) emotional response to the possibility of a gain or a reward as a non-depressed person.

When given a card-playing task designed to assess risk-taking, for example, depressed participants had a harder time remembering which options were more likely to yield rewards, making them worse at the game than non-depressed participants. Participants with depressive symptoms also were more conservative in their risk-taking than non-depressed participants – sticking with safe choices that had low chances of reward, instead of adopting higher-risk strategies with potentially larger payoffs.

These are laboratory studies, but there is some good evidence that the same effects play out in the real world. People with SAD are more likely to be conservative in their financial decisions in the winter than people who didn’t have SAD, for instance.

And when it comes to making decisions, being more risk-averse isn’t always a bad thing.

This is especially true because most healthy individuals have the opposite problem: ‘optimism bias’. Most of us believe we’re less likely to experience a negative event (like getting cancer or being in a car crash) than the statistics would warrant, and that our future is likelier to be rosier (whether in terms of getting more job offers or having a great holiday) than actually turns out to be the case. We also tend to think that we’re more in control than we really are – particularly if we’re involved in the event ourselves.

As you might expect, depressed people, who have a more pessimistic view of the world, don’t fall into this trap. This ‘depressive realism’ means they are better at accurately assessing time intervals and at predicting how other people's decisions will affect them than their more optimistic peers. They also learn to avoid risky responses faster than non-depressed people.

But that doesn’t mean they’re accurate with forecasting in general – depressed people are worse than healthy people at predicting football World Cup match results for example.

There is another twist, too. Optimists may see the future with rose-coloured glasses – but they’re also better at making that future come true. Greater optimism is associated with more career success, better relationships and better health. Long-running studies also have found that the effect seems to go beyond correlation (‘I’m optimistic because I’m in good health’) and perhaps be causation (‘My optimism helps me have good health’). One study, for example, looked at 97,000 women, all of whom had no cancer or cardiovascular disease when the study began. Eight years later, the optimists were less likely than pessimists to have developed coronary heart disease or have died of any cause.

And if you’re struggling to make a life choice, it may also be worth waiting until longer days bring a lighter mood: depressive symptoms can interfere with the decision making process that that it is harder to make any decision at all, with people with depression feeling more conflicted and indecisive than non-depressed people.

So the relationship between mood and decision-making is not a simple one – which means that if you’re considering when to make a big decision, you may want to think about what kind it is. Does it involve potentially catastrophic losses – something that may require caution and a realistic outlook? Then winter may be better. Or is it a decision where there’s everything to play for, if you can accept a certain amount of uncertainty about the outcome? Then perhaps you should take advantage of your more elevated mood in summer.

And if you feel stymied from making a choice at all, you might want to wait a bit until sunshine returns. Who knows – it may help clear up not only your mood, but your indecision.

Join 900,000+ Future fans by liking us on Facebook, or follow us on Twitter or Instagram.

If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Culture, Capital, and Travel, delivered to your inbox every Friday.