Why Watching the Clock at Night Makes Insomnia Worse

Read time: 5 minutes

What you’ll learn:

• Why checking the time at night makes it harder to fall back asleep
• What clock-watching does to your perception of how long you’ve been awake
• Why people with insomnia find it hard to stop checking, even when they know they should
• What CBT-I does about it that turning the clock around doesn’t

It’s 3:17 a.m. You know it’s 3:17 a.m. because you just checked.

Now the arithmetic starts. Alarm at 6:30, so that’s three hours and thirteen minutes. If you fall asleep right now. But you won’t fall asleep right now. You just woke yourself up enough to calculate how little sleep you’ll get. You might check again in twenty minutes. Or ten.

This is clock-watching, and it has its own research literature.

What the research shows

Researchers at Indiana University studied nearly 5,000 patients presenting at a sleep clinic and found that time monitoring behaviour, the clinical term for clock-watching, doesn’t just reflect insomnia. It makes insomnia worse (Dawson et al., 2023). The relationship runs through frustration: checking the clock generates frustration about lost sleep, that frustration amplifies arousal, and heightened arousal makes sleep harder to achieve. Patients with higher clock-watching scores were also more likely to be using sleep medication, both over-the-counter and prescription.

The effect is bidirectional. Insomnia makes people more likely to check the clock, and clock-checking makes insomnia more severe. Once that cycle starts, it tends to sustain itself.

The mental arithmetic problem

When you see 3:17 on a display, your brain does not passively register the information. It starts calculating. How many hours until the alarm? How many hours have you already lost? What will tomorrow feel like if you only sleep two more hours?

This is active cognitive processing, and active cognitive processing is the opposite of what sleep onset requires. Sleep doesn’t arrive through effort. It arrives when the nervous system settles. The arithmetic spiral does the reverse: it generates anxiety, elevates arousal, and keeps the wakefulness system running at exactly the moment you need it to quiet down.

Research by Nicole Tang and colleagues put this to a direct test. In one experiment, participants with insomnia were assigned to monitor either a clock or a neutral digit display as they tried to fall asleep. Clock monitors reported more pre-sleep worry and took longer to fall asleep (Tang et al., 2007). That part is not surprising. What is surprising is a secondary finding: clock monitors also overestimated how long they had been awake, more than the group watching a display with no time on it.

Clock-watching doesn’t just feel bad. It warps your perception of how long you’ve been lying there.

The mechanism is clear enough. Processing more information, the time, the arithmetic, the associated worry, makes subjective time feel longer. If you’ve lain awake for forty-five minutes and spent most of it calculating, it will feel like ninety. This is one reason people with insomnia consistently overestimate their sleep onset latency compared to objective measurements. In a study at the Stanford Sleep Clinic, patients overestimated how long it took them to fall asleep by an average of thirty minutes, and underestimated total sleep time by close to an hour (Jacobs, 2009). The clock is partly responsible for that gap.

Why it’s hard to stop

Here is what the advice usually looks like: just turn the clock around. Don’t look at your phone. Put your watch in the other room.

That advice is reasonable. It is also incomplete, for a specific reason that the research makes clear.

People with insomnia don’t look at the clock simply because it’s there. They look because the insomnia brain has been trained to treat nighttime time displays as a threat cue. In an experiment using a reaction-time task, researchers measured how quickly participants could disengage their attention from clocks displaying nighttime hours compared to other visual stimuli (Woods et al., 2009). People with insomnia showed significantly delayed disengagement. They were slower to look away from the clock than good sleepers. This attentional bias happened involuntarily.

This is not a failure of willpower. It is a conditioned response. Over months or years of lying awake, the mind has learned to treat the clock the way an anxious person treats a threat: by monitoring it, because monitoring threats feels like control. Checking the time feels like doing something. It’s not.

Stimulus control theory describes this precisely. Environmental cues shape behaviour through learned associations (Jacobs, 2009). For good sleepers, the bed has been paired with sleep hundreds of times, so it functions as a cue for drowsiness. For people with insomnia, the bed and the clock get paired with wakefulness, frustration, and arousal. Seeing the clock becomes a trigger. The fact that the trigger is glowing in the dark, showing numbers that mean something distressing, makes the association stronger, not weaker.

There is a practical problem with removal alone: when the bedroom clock is gone, people check the microwave on the way to the bathroom. They glance at the stove. They lift the phone, just this once, just to check. The monitoring behaviour migrates because the compulsion to track time comes from the anxiety about sleep, not from the proximity of any specific display. Smartwatch wearers have a particularly difficult version of this. The wrist is always there.

What covering the clock does and doesn’t do

Turning the clock around is a reasonable first move. Removing visual time cues reduces the probability of the trigger firing and limits opportunities for the arithmetic spiral to start. For some people, especially early in treatment, it produces a noticeable improvement.

But it works at the level of the cue, not at the level of the anxiety that makes the cue threatening. Harvey’s cognitive model of insomnia identifies selective attention and monitoring as a core maintaining mechanism, one of five processes that keep insomnia going (Harvey, 2002). Clock-watching sits squarely within that mechanism, alongside the dysfunctional beliefs about sleep that make the numbers on the clock feel catastrophic. Address only the cue and the beliefs remain untouched.

This is the gap between sleep hygiene advice and CBT-I. Sleep hygiene removes the clock. Cognitive behavioural therapy for insomnia works on the conditioned associations, the cognitive patterns that make the clock frightening, and the broader arousal system that keeps the wakefulness drive running when it should be settling.

What CBT-I addresses instead

Stimulus control in CBT-I includes clock removal, but the rationale matters more than the technique. The goal is to rebuild the bed and the night as cues for sleep rather than cues for performance anxiety. That requires consistent behaviour change across weeks, not a one-night experiment. It also requires decoupling the meaning attached to time: the belief that every hour lost is a catastrophe, that the number on the clock determines what tomorrow will be like.

The cognitive component of CBT-I addresses the sleep arithmetic directly. If you find yourself at 3:17 a.m. calculating hours to the alarm, that calculation rests on a set of assumptions about what insufficient sleep means for your functioning, your health, your day. Those assumptions are usually overstated. Working through them is not about positive thinking. It is about accuracy.

Across dozens of trials, CBT-I produces durable improvements in sleep onset latency, wake time after sleep onset, and sleep efficiency without the risks associated with long-term sleep medication use. For people who have been waking at 3 a.m. for months, running the same mental arithmetic every night, not having that spiral available to fall into is no small thing.

Turning the clock around is a start. Understanding why the clock became a problem in the first place is where the work is.

TL;DR

• Checking the time at night makes insomnia worse by triggering a mental arithmetic spiral. Calculating hours left until the alarm generates frustration and elevates arousal at exactly the wrong moment.
• Clock-watching distorts time perception. Research shows people who monitor the clock overestimate how long they’ve been awake compared to those watching a display with no time on it. Time feels longer when you’re actively processing it.
• The difficulty stopping is not a willpower problem. Studies show people with insomnia have an involuntary attentional bias toward nighttime clock displays. Their brains have been trained to treat the clock as a threat cue, and disengaging is harder for them than for good sleepers.
• Removing the clock helps at the level of the trigger. But the anxiety that makes the clock threatening remains. The monitoring behaviour tends to migrate to other displays when one is removed.
• CBT-I works at a deeper level, rebuilding sleep-related associations through stimulus control and addressing the cognitive patterns that make the numbers on the clock feel catastrophic.

Start here

If you’ve been waking in the night and spending the next two hours running the numbers, that pattern is worth addressing properly. Clock removal is a reasonable first step. CBT-I is how you get to the point where the clock stops mattering.

I offer virtual CBT-I across British Columbia. Book a free 15-minute consultation to talk through what that would look like for you.

About the author

Graeme Thompson, MA, RCC (Registration #21951, BCACC) is a Registered Clinical Counsellor practising virtual CBT-I across British Columbia. BC CBT-I is a specialist practice. CBT-I is the only thing he does. Learn more about the practice.

References

Dawson, S. C., Krakow, B., Haynes, P. L., Rojo-Wissar, D. M., McIver, N. D., & Ulibarri, V. A. (2023). Use of sleep aids in insomnia: The role of time monitoring behavior. The Primary Care Companion for CNS Disorders, 25(3), 22m03344. https://doi.org/10.4088/PCC.22m03344

Harvey, A. G. (2002). A cognitive model of insomnia. Behaviour Research and Therapy, 40(8), 869–893. https://doi.org/10.1016/S0005-7967(01)00061-4

Jacobs, G. D. (2009). Say goodnight to insomnia. Holt Paperbacks.

Tang, N. K. Y., Schmidt, D. A., & Harvey, A. G. (2007). Sleeping with the enemy: Clock monitoring in the maintenance of insomnia. Journal of Behavior Therapy and Experimental Psychiatry, 38(1), 40–55. https://doi.org/10.1016/j.jbtep.2005.07.004

Woods, H., Marchetti, L., Biello, S., & Espie, C. (2009). The clock as a focus of selective attention in those with primary insomnia: An experimental study using a modified Posner paradigm. Behaviour Research and Therapy, 47(3), 231–236. https://doi.org/10.1016/j.brat.2008.12.001

Wu, J. (2023). Hello sleep: The science and art of overcoming insomnia without medications. St. Martin’s Essentials.