Deep Work in 25-Minute Blocks? You're Doing It Wrong

Why can’t I focus on deep work for more than 20 minutes?

You’ve tried the Pomodoro Technique—25 minutes of work, 5 minutes of rest—but somehow you still end up doom-scrolling by the third session. You’ve read Cal Newport’s Deep Work and nodded along, but your calendar is a swamp of meetings and “quick tasks.” The problem isn’t your willpower. It’s that you’re using the wrong tools in the wrong order. Deep work isn’t about gritting your teeth for longer stretches; it’s about designing your day so that focus becomes the default, not the exception.

The Pomodoro trap: why 25-minute sprints backfire for deep work

Francesco Cirillo invented the Pomodoro Technique in the late 1980s as a burned-out university student in Rome, naming it after his tomato-shaped kitchen timer. The method is simple: work for 25 minutes, break for 5, and take a longer 15–30 minute break after four cycles. That structure works great for clearing emails or filing expense reports—shallow tasks that don’t require deep cognitive lifting. But for deep work—the kind that demands sustained, undistracted focus on a cognitively demanding task—a 25-minute sprint is just enough time to get into the weeds before the timer yanks you out.

Here’s the kicker: the Pomodoro’s rigid break interrupts the very state you need to cultivate. Flow, the state where you’re so absorbed that nothing else matters, requires a match between challenge and skill. You don’t hit flow in 25 minutes; you hit it after 30, 40, or 60 minutes of unbroken concentration. By forcing a break at 25 minutes, you’re cutting off the flow state before it fully blooms. That’s why so many people report that Pomodoros feel like they’re getting things done, yet the big, important projects never seem to move forward.

I’m not saying the Pomodoro is useless. It’s a fantastic tool for getting started when you’re procrastinating, and it’s excellent for shallow tasks. But if your goal is deep work, you need to rethink your approach.

Time blocking: the real deep work strategy

Cal Newport, the Georgetown computer science professor who popularized time blocking, argues that “a 40-hour time-blocked work week produces the same amount of output as a 60+ hour work week pursued without structure.” That’s a bold claim, but it aligns with what the research on attention says. When you switch between tasks, you pay a heavy toll. The American Psychological Association’s research found that task-switching can cost up to 40% of productive time, and the mental blocks get worse with complexity. Even worse, Sophie Leroy’s 2009 study showed that unfinished tasks leave “attention residue” that impairs your performance on the next task. So if you’re flitting between Slack, email, and your “real” work, you’re never fully present for any of it.

Newport’s method is to divide your day into blocks—typically 30 minutes to several hours—and assign each block to a specific task or group of similar tasks. Crucially, he protects blocks of 90 minutes to 4 hours for deep work. That’s the sweet spot. In that kind of block, you can get past the initial resistance, enter flow, and actually make progress on something that matters.

But time blocking alone isn’t enough. You also need to defend those blocks. Gloria Mark’s research at UC Irvine found that it takes an average of 23 minutes and 15 seconds to fully regain focus after a single interruption, and that workers are interrupted or switch activities on average every 3 minutes and 5 seconds. That’s a recipe for never reaching deep work. So when you block out 90 minutes, you have to treat it like a meeting with your most important client—because you are that client.

Parkinson’s Law: the secret weapon for deep work

Here’s where most people get stuck. You block out 2 hours for deep work, but you still waste the first 30 minutes checking Twitter “just to clear your head.” The solution isn’t more discipline; it’s more constraint. Parkinson’s Law states that “work expands so as to fill the time available for its completion.” This was coined by Cyril Northcote Parkinson in a 1955 essay for The Economist, where he observed that bureaucracies grow regardless of the actual workload. But the law works in reverse too: if you give yourself less time, you’ll get the work done faster.

So instead of blocking out 2 hours for a deep task, try blocking out 90 minutes. Or even 60. The research on the planning fallacy—the bias where we underestimate how long things take—suggests we’re terrible at estimating how long a task will take, but we can use Parkinson’s Law to our advantage by setting shorter, ambitious deadlines. You’ll be surprised how much you can get done when the clock is ticking.

One word of caution: don’t set deadlines so tight that you sacrifice quality. The goal is to create a sense of urgency, not panic. A good rule of thumb is to take your initial estimate and cut it by 20–25%. That’s enough to keep you focused without making you sloppy.

The perfect deep work day: a concrete plan

So how do you actually put this together? Here’s a concrete example, based on the research and the methods I’ve described. Let’s say you’re a writer working on a book chapter. You’ve decided to write 1,500 words of serious prose today. Here’s what your morning could look like:

• 7:00 AM: Wake up, no phone. Eat breakfast, review your calendar.
• 8:00 AM: Start your first deep work block. Turn off all notifications, close your email, and put your phone in another room. Set a timer for 60 minutes.
• 9:00 AM: Take a 10-minute break. Stand up, stretch, get water. Do not open social media.
• 9:10 AM: Second deep work block, 60 minutes. Write until the timer rings.
• 10:10 AM: Longer break, 15 minutes. Then a 90-minute block for deep work on the most challenging section.

That’s 3.5 hours of deep work before lunch, and you’ve planned it all in advance. Notice the gaps between blocks—those are for transitions, not for drifting. And notice that I didn’t schedule a single Pomodoro. The blocks are longer because the task is cognitively demanding.

Quick tip: If you’re prone to checking your phone during breaks, use that time to move your body or do a quick mindfulness exercise. A 2025 study found that 90-second micro-breaks every 10 minutes can boost performance, but those are for vigilance tasks, not for a 60-minute writing sprint. For deep work, a 10–15 minute break between blocks is plenty.

What I’d actually do

If you take away one thing, it’s this: stop using Pomodoros for deep work. Instead, use time blocking to schedule 60–90 minute blocks for your most important tasks, and apply Parkinson’s Law to keep them tight. And don’t forget the power of a proper break—your brain needs to recharge, not just switch tabs.

Here’s my blunt recommendation: choose one deep work task that you’ve been avoiding, block out 90 minutes tomorrow morning, and commit to doing nothing else during that time. No email, no Slack, no “just checking” anything. When the 90 minutes are up, take a real break. Then, at the end of the day, review what you accomplished and adjust your blocks for the next day. Do this for a week, and you’ll see a difference.

Remember, deep work isn’t about grinding for hours on end. It’s about creating the conditions where focus can flourish. That means planning your day, protecting your attention, and giving yourself the time to get into the zone. You’ve got this.

Sources

• Time management methods (Wikipedia) - https://en.wikipedia.org/wiki/Time_management
• Pomodoro Technique (WVU Online) - https://online.wvu.edu/news-and-stories/2026/03/19/the-pomodoro-technique-helping-online-students-get-things-done
• Deep Habits (Cal Newport) - https://calnewport.com/deep-habits-the-importance-of-planning-every-minute-of-your-work-day/
• Parkinson's Law (BBC Worklife) - https://www.bbc.com/worklife/article/20191107-the-law-that-explains-why-you-cant-get-anything-done
• APA: Multitasking - switching costs - https://www.apa.org/topics/research/multitasking
• Leroy 2009 attention residue (IDEAS/RePEc) - https://ideas.repec.org/a/eee/jobhdp/v109y2009i2p168-181.html