Does Multitasking Work? The Hidden Cost of Switching

Answering emails during a meeting, checking messages while writing a report, scrolling a feed while half-watching a film: it feels efficient, as if two things are getting done at once.

For most tasks that take thought, they aren’t. Your brain switches between them, and each switch costs a little time to get back up to speed. The costs are small enough to feel like nothing and large enough, over a day, to matter a great deal. Set the switches in the toy at the top and watch the minutes add up.

Two things at once, or one after another?

Some things really can be done together: walking and talking, or folding laundry while listening to music. One of them runs on autopilot, so it barely needs attention.

But two tasks that both need attention, like reading and writing, or listening to a colleague and replying to an email, can’t truly run side by side. What feels like doing both is your attention hopping back and forth between them, so quickly that you don’t notice the gaps.

The giveaway is what happens to the quality. Try to follow a conversation while reading a message, and you’ll find you’ve missed a sentence of one or the other. That’s not carelessness. It’s the bottleneck that sits at the centre of how attention works.

The switch cost

Every time you switch, you have to drop one set of goals and rules and pick up another: where was I, what was I about to do, what does this need? Psychologists call the time this takes the switch cost.

In a series of experiments published in 2001, Joshua Rubinstein, David Meyer and Jeffrey Evans had people switch between tasks such as solving maths problems and sorting shapes. Switching always took longer than sticking with one task, and the cost grew as the tasks got more complicated or less familiar. Each switch cost only fractions of a second in the lab. Meyer has estimated that in real work, with constant switching between complex tasks, the losses can reach as much as 40% of someone’s productive time.

In real offices, the cost of getting back in is much longer than a lab switch. The researcher Gloria Mark has studied people at work and found that after an interruption, it can take a long time, often more than twenty minutes, before people return to what they were doing, because one interruption tends to lead to another.

The cost you don’t see

Switching doesn’t only add time. It also delays everything.

Do two half-hour tasks one after another and the first is finished at 30 minutes. Switch between them and the first isn’t finished until near the very end. If the first was the one someone was waiting for, switching made them wait almost twice as long, for no gain at all.

There’s also the cost of mistakes. When attention is split, people are more likely to miss details, and checking and fixing errors takes more time again. And there’s what the researcher Sophie Leroy calls attention residue: when you leave a task unfinished, part of your mind stays on it, so you do the next task less well. Her experiments found people performed worse on a new task when they’d been pulled away from an unfinished one.

A morning, two ways

Picture a morning with a report to write and an inbox that pings about every ten minutes.

In the first version, you answer each email as it arrives. Each one takes three minutes, but getting back into the report takes another five, because you have to reread where you were and remember what you meant to say next. Over three hours, eighteen emails cost you about 54 minutes of replying and another 90 of getting back in. The report gets about half of the morning, in broken pieces, and it shows.

In the second version, you turn the notifications off, write for ninety minutes, then answer all the emails in one forty-five-minute block. Then you write for another forty-five minutes. The same emails get answered, slightly later. The report gets more than two hours of continuous attention, and you finish it.

The numbers are illustrative, but the shape is what studies find: the replies take the same time either way. What changes is everything around them.

Why we keep doing it

If it’s so costly, why is it so tempting? Partly because switching feels productive. Each email answered is a small, visible win, and it’s satisfying in a way that slow progress on a hard task isn’t. Partly because new things grab attention, so a fresh notification is hard to ignore. And partly because of social pressure: in many workplaces, fast replies are taken as a sign of being good at the job, even when they come at the cost of the work that matters.

Knowing this doesn’t make the urge go away. It does make it easier to set up your day so that you have to resist it less often.

Are some people good at it?

Some people feel they are. A 2009 study by Eyal Ophir, Clifford Nass and Anthony Wagner at Stanford compared people who said they multitasked heavily with media against those who rarely did. The heavy multitaskers were, if anything, worse at ignoring irrelevant information and at switching between tasks.

There is a very small group who seem to manage it.

Feeling good at multitasking, in other words, isn’t the same as being good at it, and the people most confident in their skill are often the ones it most misleads.

In class and on the road

Two settings show what’s at stake.

Learning. In a 2013 study, Faria Sana and colleagues had students attend a lecture with laptops. Those asked to do a few unrelated online tasks during the lecture scored lower on a test of it afterwards. So did students who weren’t multitasking themselves but could see a classmate’s screen. Distraction spreads.

Driving. Driving feels automatic, but it isn’t, especially when something unexpected happens.

Working with fewer switches

You don’t need perfect focus. You need fewer switches, and better ones.

• Batch similar tasks. Answer emails in two or three blocks a day instead of as they arrive. Make calls in a row.
• Turn off notifications for the length of a piece of focused work. Each one invites a switch, even if you don’t act on it.
• Finish the thing someone’s waiting for first. Switching delays everything; doing one thing at a time gets each one out sooner.
• Leave yourself a note when you must switch: where you were and what was next. It shortens the time to get back in and reduces the residue.
• Protect blocks of deep work. An hour or two with no meetings and no messages does more than a day of fragments.
• Keep the phone out of reach. Studies suggest that even a phone face down on the desk can draw some attention away from the task.
• Let easy tasks pair up. Folding laundry while on a call, or walking while listening to a podcast, is fine. Save your attention for things that need it.

When switching is the job

Some jobs are made of interruptions: a nurse on a ward, a parent of small children, a support desk. In those, single-tasking isn’t on offer. What helps there is reducing the cost of each switch: checklists that hold your place, clear handovers, writing things down so that your memory isn’t doing the job of a notebook. The principle is the same. Every time you leave a task, make it easier to come back.

Test yourself

The free how learning works test covers how attention and practice really work, and the psychology myths test has more beliefs about the mind to check, including the one about doing two demanding things at once.