Attention Residue: Why Multitasking Costs You 40% and How to Stop

In 2009 Sophie Leroy, an organizational-behavior researcher at the University of Washington, published a paper with a name that sticks: 'Why is it so hard to do my work?' The finding was that when you switch from Task A to Task B, part of your attention stays on Task A, she called it attention residue, and the residue degrades your performance on Task B in measurable ways. Fifteen years later, dozens of replications and extensions have made the same point more strongly: humans are bad at multitasking not because we lack discipline, but because our attention has physics.

The productivity cost is roughly 20–40% per switch, depending on the depth of the tasks involved. Switch between three cognitive tasks in a morning and you've lost half your working capacity to residue alone. This is why a two-hour meeting followed by 'focused work' rarely produces focused work.

Why 'just focus' doesn't work

The residue is not a willpower problem, it's an interrupted-cognition problem. Any task you leave unfinished (or worse, unresolved) leaves an open cognitive loop the brain keeps checking on. This is the Zeigarnik effect, discovered in the 1920s, dressed in modern clothes. You can't just decide to close the loop. You have to actually close it, or park it explicitly.

The three moves that reduce residue

• The parking sentence: before you switch tasks, write one sentence about the next step on the task you're leaving. This closes the loop for your brain because there's now a known re-entry point on paper.
• The 30-second reset: between tasks, stand up, take three breaths, then start the new task. Sounds trivial. It works because it interrupts the default-mode network's tendency to keep chewing on whatever you just left.
• The batching principle: cluster similar tasks (all Slack replies, all emails, all shallow admin) into one block rather than sprinkling them through the day. Switching within a batch has near-zero residue cost; switching between deep and shallow modes has the highest.

The single biggest lever: end your workday on paper

The 5 p.m. brain dump is the most under-rated productivity practice in the modern literature. Spend 3 minutes at the end of your workday writing down every open loop, what you left unfinished, what you're worried about, what tomorrow's first task is. That single sheet closes the residue for the evening, which is why people who do it consistently report sleeping better and having more presence at home.

"You have to stop working before you stop working."

, Cal Newport

Inbox and Slack: the concrete rules

The average knowledge worker checks Slack every 4 minutes and email every 6 minutes. Each check triggers a small residue event. The fix isn't heroic. It's mechanical: turn off both notifications at the OS level (not the app level, the OS level). Check Slack in three defined windows: mid-morning, post-lunch, end of day. Check email twice: 10:30 and 15:30. Announce this in your Slack status once and then just do it. Nobody will notice for the first three days. By the end of week one, you'll have recovered roughly 90 minutes of focus per day.

The meeting rule

A one-hour meeting doesn't cost you an hour, it costs you roughly 90 minutes when you count the residue on either side. This is why five meetings in a day feel like a full day even if you only sat in meetings for four hours. The practical implication: refuse to schedule any meeting for longer than 30 minutes without a clear reason, and cluster meetings back-to-back rather than sprinkling them, because the residue cost is per-transition, not per-meeting.

The one-line version

Every task switch costs you 20–40% until you close the loop. Write the parking sentence, batch similar work, and do a 5 p.m. brain dump. That's most of the game.