Why Multitasking Makes You Slower, Not Faster
Answering messages during a call, or flipping between a report and an inbox every few minutes, feels like getting more done at once. For most demanding work, the evidence says the opposite: switching between tasks costs time and accuracy, and the cost is easy to miss because each switch feels so small.
This is what is actually going on in the brain, what the research found, and what works better without turning your day into a rigid schedule.
The brain switches, it does not split
For tasks that need real thought, the brain does not run two of them in parallel. It alternates quickly between them, a process researchers call task switching. Each time, it has to disengage from the rules and context of one task and load those of the other.
That is different from doing something automatic alongside something that needs attention. Walking while talking works because walking costs almost no conscious effort. Writing an email while following a conversation does not, because both need the same kind of attention.
What a switch costs
In a well-known set of experiments published in 2001, researchers Rubinstein, Meyer, and Evans measured how long people took to complete tasks when they had to switch between them. Switching cost time every time, and the cost grew with the complexity of the tasks. A single switch cost only fractions of a second in simple tasks, but real-world work involves complex tasks and hundreds of switches a day.
You will often see a claim that task switching costs “up to 40 percent” of productive time. That figure is a rough popular summary, not a number measured in a single controlled study, so treat it as an illustration. The direction of the finding, that switching has a cost, is consistent across the research.
Attention residue: part of your mind stays behind
Part of the cost is not the switch itself but what it leaves behind. Business researcher Sophie Leroy described “attention residue” in 2009: when you move from task A to task B without finishing A, part of your attention remains stuck on A, and your performance on B suffers.
The residue is worse when task A was left unfinished. This is why checking one more message in the middle of focused work can ruin the next twenty minutes even if the message itself took ten seconds.
Interruptions take a long time to recover from
Researcher Gloria Mark and colleagues at the University of California, Irvine studied how people work in real offices. A figure that is quoted constantly is that it takes about 23 minutes to get back to a task after an interruption. That exact number is repeated more often than it is verified, and it traces back to interviews and workplace studies rather than a single controlled experiment. Her published workplace studies report the same order of magnitude, roughly 25 minutes to return to the original task, usually after doing other things in between. The pattern matters more than the exact figure: recovery is slow and incomplete.
Why it feels productive anyway
Constant switching produces a stream of small completions: a reply sent, a notification cleared, a tab closed. Each one brings a small sense of progress. The brain registers many quick wins, and that feeling can persist at the end of a day even when the one important task did not move.
This is the same trap described in the real reason to-do apps don’t fix procrastination: the activity that feels like progress and the activity that produces results are often different things.
What heavy multitaskers lose
A 2009 study from Stanford, led by Ophir, Nass, and Wagner, compared people who regularly use many media streams at once with those who do not. The heavy multitaskers did worse, not better, on tests of filtering out irrelevant information and of switching between tasks. The researchers’ interpretation was that people who practice constant switching become more easily distracted, not more capable. Later attempts to replicate the finding have been mixed, and the original groups were small, so it is better read as suggestive than settled.
There are exceptions. A 2010 study by Watson and Strayer, using a driving simulator combined with a memory-and-math task, found a small group, 5 of 200 participants or 2.5 percent, who showed no drop in performance when doing both. They are rare enough that planning your own day around being one of them is a bad bet.
When doing two things is fine
- One task is automatic. Walking and talking, or folding laundry while listening to a podcast.
- The tasks use different resources. Listening to instrumental music while doing routine work.
- Neither task is important. Mistakes cost little, so the penalty does not matter.
How to cut switching without a rigid schedule
- Batch the small stuff. Check email and messages at set times instead of continuously. Even two or three windows a day are enough for most roles.
- Write a “resume note” before you switch. A 2018 follow-up by Leroy and Theresa Glomb found that a short “ready-to-resume” plan, a quick note on where you stopped and what comes next, reduced attention residue and made it easier to return.
- Use a timer for focus blocks. Twenty-five to fifty minutes on one thing, then a break, is enough to get most of the benefit.
- Remove the easy switches. Phone out of reach, one browser tab for the task, notifications off during the block.
- Clear tiny tasks in the gaps. The method in the two-minute rule works best between blocks, not in the middle of them.
Quick answers
Is it multitasking if I switch quickly between two tasks?
Yes. Fast switching is still switching, and it carries the same costs. It only looks like doing both at once.
What about jobs that require responding quickly to many people?
Some roles genuinely require constant availability. Even there, protecting one or two short blocks for work that needs depth usually pays off.
Does background music count?
It depends. Music without lyrics usually has little effect on routine work, while lyrics can interfere with reading or writing.
The short version
- Demanding tasks are not done in parallel; the brain switches, and each switch has a cost.
- Part of your attention stays on the task you left, which hurts the next one.
- Heavy multitaskers tend to get worse at filtering distractions, not better.
- Batching, resume notes, and focus blocks reduce the cost without making work rigid.
Sources
- Rubinstein, J. S., Meyer, D. E., and Evans, J. E. (2001). Executive control of cognitive processes in task switching. Journal of Experimental Psychology: Human Perception and Performance. Link
- Leroy, S. (2009). Why is it so hard to do my work? The challenge of attention residue when switching between work tasks. Organizational Behavior and Human Decision Processes. Link
- Mark, G., Gudith, D., and Klocke, U. (2008). The cost of interrupted work: more speed and stress. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. Link
- Ophir, E., Nass, C., and Wagner, A. D. (2009). Cognitive control in media multitaskers. PNAS. Link
- Watson, J. M., and Strayer, D. L. (2010). Supertaskers: profiles in extraordinary multitasking ability. Psychonomic Bulletin and Review. Link
- Leroy, S., and Glomb, T. M. (2018). Tasks interrupted: how anticipating time pressure on resumption of an interrupted task causes attention residue and low performance on the interrupting task and how a ready-to-resume plan mitigates the effects. Organization Science. Link
