Huberman's 90-Minute Focus Block: What He Says and What the Research Shows

What Huberman actually says

The advice comes from his Focus Toolkit episode (September 2022). Here’s what he recommends:

• Work in blocks of about 90 minutes or less. He’s clear that you don’t have to do the full 90 and that pushing for two or three hours straight isn’t the goal.
• Count the warm-up. The first 5 to 10 minutes are a transition and they’re part of the 90. It’s normal for your focus to drift early on.
• Do two, maybe three a day. If you’re new to it he suggests one a day for about four weeks before adding more.
• Defocus afterwards. Take at least 10 minutes and up to 30 of what he calls deliberate defocus: low-effort time where your mind can wander.
• Keep your phone away on the break. Even if you’re just walking down the hall. The point is to let your attention rest.

Where does the 90-minute idea come from?

It goes back to Nathaniel Kleitman, the sleep researcher who helped discover REM sleep. During sleep your brain moves through cycles of roughly 90 minutes. Kleitman proposed a “basic rest-activity cycle” that keeps running through the day too. If he was right, alertness would rise and fall on a similar rhythm while you’re awake. These are called ultradian rhythms: cycles shorter than a day.

Is the 90-minute ultradian cycle real?

For sleep, yes. For waking hours, it’s much less certain. Some studies have found rhythms of roughly 90 minutes in alertness and attention. Others haven’t. One study by Okudaira, Kripke and Webster tracked people’s movement through the day and found no 90-minute cycle at all. Its title says so plainly.

So I wouldn’t time your day around a 90-minute clock in your brain. The useful parts of Huberman’s advice don’t depend on it anyway. A warm-up, a limit on how long you push, a real break and a daily cap all make sense on their own.

How to run a 90-minute focus block

1. Pick one task worth 90 minutes. Choose the hardest or most important thing on your list. Write it down so you know what the block is for.
2. Put your phone away. Block your distracting apps or leave the phone in another room for the whole block and the break after it.
3. Start the timer and ride out the warm-up. Set 90 minutes, or less if you're new to long blocks. Expect the first 5 to 10 minutes to feel scattered. Keep bringing your attention back.
4. Stop when the block ends. Don't keep going past the timer, even if it's going well. Huberman's advice is to stop at 90 minutes or sooner.
5. Defocus for 10 to 30 minutes. Walk, get water, do something routine or just sit. Keep your phone away so your attention can idle.
6. Do two, maybe three a day. Start with one block a day for about four weeks. Then add a second. Don't go past three.

The free 90-Minute Focus Timer runs this for you. It starts the break on its own and has shorter 60/15 and 45/10 presets while you build up.

What deliberate defocus looks like

The break is where most people slip. Checking your phone feels like rest but it keeps your attention busy. Try one of these instead:

• A short walk, inside or out
• Getting water or making tea
• Something routine with your hands, like a few dishes
• Sitting and looking out a window
• Lying down with your eyes closed

90-minute blocks vs 52/17 vs Pomodoro

If 90 minutes feels like too much, the 52/17 rule is a good middle ground.

Keep your phone out of both halves

Huberman’s advice keeps coming back to the phone: away during the block and away during the break. That’s the hard part. I built Kappi, a screen time blocker for iPhone, to make it easier. Start a focus session and Kappi blocks the apps you choose with Apple’s Screen Time until it ends. Stay on task and Kappi is happy.