Why more women carry the 'mental load' - and how couples can share it

"My head's always full," says mum-of-three Stacie Matthias. "I go to sleep with a mental to-do list."

She's talking about the concept of the "mental load" - the burden of planning, organising, remembering and anticipating tasks that keep a household running.

These tasks include: remembering school trips, checking for updates in parents' WhatsApp groups, noticing which parts of the house need cleaning, monitoring how much sleep children get, scheduling doctors' appointments and buying school uniforms.

According to academics, this is work that in heterosexual couples disproportionately falls to women - particularly mothers - alongside the bulk of physical household labour.

All relationships and households are different, of course, but studies suggest clear patterns.

Children in the UK have just gone back to school from the summer holidays, and Stacie, 37, from Stockport, says her mind often feels especially busy in September.

"It's that feeling of always having something to remember, organise or worry about that makes this time of year particularly full-on," she says.

For Stacie this list of responsibilities leaves her mind feeling like a washing-up bowl that's being filled up throughout the day.

"If someone's not helping you remove those pots and pans, your water's overflowing by the end of the day," she says, "and you're at tipping point."

In a survey looking into the mental load that involved 3,000 US parents, academics at the University of Bath and the University of Melbourne , externalfound that mothers handled 71% of household tasks that required mental effort, such as keeping track of when sheets and towels needed to be washed and remembering by when food in the fridge needed to be eaten.

The study found that fathers handled many of the tasks researchers described as "episodic" - things that happen less often, such as remembering when to get the car serviced.

University of Melbourne Prof Leah Ruppaner describes the mental load as being invisible, enduring and without boundaries. "You don't bring your dishes to work, but you bring the mental load everywhere," she says.

The mental load is a popular topic on forums like Reddit and Mumsnet, where women seek advice about how to talk to their partners about the exhaustion of trying to juggle so many different responsibilities.

Mums told BBC News they were often added to school WhatsApp groups - where parents discuss things like non-uniform days, school trips, birthdays and lost property - as the "default parent", while their partners never joined.

Sophia, a 35-year-old mum of three in Portsmouth, pays for school trips and makes lunch orders on her children's school's app on her phone, but says her husband has never downloaded it.

Sophia says she tried multiple times to explain the concept of the mental load to her husband - but feels he didn't understand and dismissed her concerns as "quick tasks".

"They are quick tasks if you could just do the task," Sophia says, "but I have to plan for the task, I have to anticipate the task, I have to be 10 steps ahead all the time."

Sam Berry, a deputy headteacher, content creator and married dad of two in London, says when his wife first raised the idea of mental load after his eldest was born, he "didn't really get it" and was "a bit defensive" because he thought he was doing a lot - changing nappies, feeding the baby and more.

He would ask what he could do to help, but he says that still puts the burden on the other person to do the thinking.

As Stacie explains: "I always say to my partner: 'If I have to ask you to do something, that's just adding to my mental load'."

It took a few months of talking and listening for Sam to understand that it was not only about completing the task, but the thinking around it - not just cooking dinner, but what food was in the house, planning the meal, and doing the shopping.

Clinical psychologist Natasha Wallace says some women come to her feeling stressed by the pressure they feel to organise their households.

"It's often, for them, not one enormous stressor," she says. "It's when they realise that they have hundreds of tiny demands on them and their brains and bodies just can't switch off."

Many women are running on autopilot, she adds, so they often don't realise the extent of the cognitive load they're carrying, and this constant low-level stress can have an effect on the nervous system. In turn, this can cause poor sleep, irritability and decision fatigue, she says.

Anita Cleare, parenting expert and author of The Work/Parent Switch, said the overall cognitive drain spills over into our work lives and leads to unsustainable burnout.

One piece of research found , externalthat men who earned more did less physical and cognitive labour related to the household, but that when women's earnings increase, they do less physical housework but still the same amount of cognitive labour.

Women very seldomly feel it is a choice to opt out of family life, so the choice then becomes whether to decelerate their career, go part-time, or stop and stay home - with more and more women making that decision, Cleare says.

"If you lower the domestic load, if you lower the mental load, you will create energy, capacity, interest in being able to perform more and better at work."

Many of the women the BBC interviewed said they believed the disparity began with maternity leave.

Wallace says that because women typically take much longer for maternity leave than dads do for paternity leave, they become the "default parent" very early on.

"If you become the person who knows everything, knows where everything is and has in the past done everything, everybody starts coming to you for everything," she says, "so you remain that central person even if you return to work."

In the UK, mothers can take up to 52 weeks of statutory maternity leave, 39 of which can be paid, while fathers can take up to two weeks of leave with statutory paternity pay. Parents can also take shared parental leave.

Some employers offer extra parental leave to their workers, but most people earn less when on maternity or paternity leave, which affects how much leave many fathers take.

Cleare says workplaces can help by making examples of fathers taking paternity leave, not just offering it, and by setting expectations around when employees are contactable, and supporting career conversations for women.

It can also come down to what are seen as traditional roles.

Zach Watson, a married father of three and coach in the US on sharing the mental load, says his grandfather might never have cooked a meal in his married life, while his father did only a little.

In the first five years of his marriage, his wife cooked most of the time. If he offered to cook, he would ask her what she wanted - a question that could actually add to her mental load.

He learned he could come to her with options for dinner, having already looked in the fridge, and give her a default if she wanted to opt entirely out of decision-making. And if he needed help, instead of just asking "Where's the ketchup?", he could explain where he had already looked.

Sam Berry says while some men do not care, a big group - his audience online - "actually are really good husbands, are really good dads, they are trying their best and want to do the best they can, but almost haven't seen it or don't have the language".

Many women the BBC spoke to were keen for their partners to take ownership of certain tasks.

Sam calls this taking on "a category of tasks" - so dad might handle all the school admin, while mum manages the food.

However, he says equality is not necessarily about splitting everything 50/50 - because one partner might work more and another might like cooking - but about finding what works best for both partners.

And if you traditionally hold more of the mental load, you might need to accept that your partner may do things very differently, and it might not always go smoothly, says Afua Williams, 40, a mother of two in London.

Those who spoke to BBC News shared their own tips about how to manage the mental load equally: