90 minutes timer

What a 90-minute timer is good for

Ninety minutes is the length of a football match, a feature-shorter film, and, most usefully, one full ultradian cycle, the natural rhythm in which the brain and body alternate between higher and lower arousal across the day. Working in ninety-minute blocks followed by a real rest is one of the most evidence-aligned ways to structure demanding cognitive work.

• •One full ultradian deep-work cycle, then a real break
• •A film, football match, or long event
• •An extended exam section or mock paper
• •A long-form writing, coding, or design session
• •A 90-minute class, seminar, or workshop block

Ultradian rhythms and the 90-minute work cycle

Your body runs on more than the 24-hour circadian clock. Throughout the day it also cycles through shorter 'ultradian' rhythms of roughly ninety minutes, alternating between periods of higher alertness and periods where focus naturally dips and the body signals for rest. The same ninety-minute cycle that governs the stages of sleep continues, in a muted form, while you are awake. Performance researchers, notably in the work popularised by Tony Schwartz and drawing on Nathan Kleitman's sleep research, argue that the most productive way to work with this rhythm rather than against it is to treat ninety minutes as a single, fully-committed work cycle, phone away, one task, no interruptions, and then to genuinely rest for fifteen to twenty minutes before the next one. The rest is not optional padding; it is what lets the next cycle start near the top of the arousal curve instead of partway down it. People who push straight through the natural dip with caffeine and willpower tend to produce a long tail of low-value work and end the day exhausted, while those who ride the cycle do less total time but more actual output.

How this 90-minute timer stays accurate

Most browser timers drift, because they count by accumulating small ticks, and browsers deliberately slow those ticks down in background tabs to save battery. This one is different: the moment you press start it records the exact wall-clock time the countdown should end, and every frame it simply measures how long is left until that fixed end time. If you switch tabs, lock your phone, or the tab is throttled, the remaining time is recomputed from the real clock the instant you come back, so a 90-minute timer is still a 90 minutes timer rather than however long the throttled ticks happened to add up to. On phones the page asks for a screen wake lock while the countdown is running, where the browser allows it, so the display does not sleep mid-count. The alarm is synthesised in the browser with the Web Audio API, which means there is no audio file to download and the chime is ready the moment you start.

Other timer lengths

Need a different length? These are the timers people most often reach for alongside a 90-minute timer:

• 1 hour timer
• 45 minutes timer
• 2 hours timer

Frequently asked questions

What is a 90-minute ultradian cycle?

It is the roughly 90-minute rhythm in which your body alternates between higher and lower alertness across the day, the waking continuation of the cycle that structures sleep. Working in 90-minute blocks with real breaks aligns effort to your natural peaks.

Should I really take a break after 90 minutes?

Yes. The 15-to-20-minute break after a 90-minute block is what lets the next cycle start fresh. Pushing through the natural dip with willpower tends to produce a lot of low-quality work and leaves you drained.

Is 90 minutes a standard film or match length?

A football match is 90 minutes of play (plus stoppage), and many films run around 90 minutes, so it is a familiar block. For deep work it doubles as one full ultradian cycle.

Does the 90-minute timer work offline?

Yes. Once the page has loaded, the countdown runs entirely in your browser using your device clock, so it keeps working with no connection. The alarm is generated in the browser too, so there is no sound file to download.