How to Keep a Sleep Diary (and What It Reveals About Your Insomnia)

Drift Sleep Guides · Updated 1 August 2026 · 8 min read

Before any gadget existed, sleep medicine had one indispensable measurement tool, and it still does: the sleep diary. It is what the NHS suggests you bring to a GP appointment about sleep problems, and it is the engine of cognitive behavioural therapy for insomnia (CBT-I) — the treatment recommended first-line for persistent insomnia, ahead of sleeping tablets (NHS — Insomnia; NICE Clinical Knowledge Summary).

A diary works because insomnia hides in patterns that single bad nights obscure. Kept honestly for a couple of weeks, it answers questions no amount of lying awake at 3 am worrying can: how much you are actually sleeping, what your real problem is (falling asleep? staying asleep? waking too early?), and which habits are feeding it.

What to record each morning

The research-standard format is the Consensus Sleep Diary (Carney et al., 2012), developed so that insomnia studies worldwide measure the same things. Its core fields, in plain terms:

For everyday self-tracking you can simplify to bedtime, wake time, quality and factors — that lighter format is exactly what Drift logs in a few taps, and it is enough to compute duration, consistency and sleep debt. If you are preparing for a GP appointment or starting CBT-I, capture the fuller set in the notes.

The three rules of a trustworthy diary

1. Fill it in within an hour of getting up, every day. Accuracy collapses when you back-fill days later — and the nights you skip are usually the bad ones, which biases the record exactly where it matters (Sleep Foundation — Sleep Diary).
2. Estimate; never watch the clock. Checking the time during the night feeds the frustration that keeps insomniacs awake. "About 40 minutes" is genuinely all the precision the method needs — the Consensus Sleep Diary itself is built on morning estimates.
3. Keep it for at least one week, ideally two. One week reveals your weekday/weekend pattern; two provide a stable baseline. Clinicians typically ask for 7–14 days before drawing conclusions.

What your diary reveals

1. Your sleep efficiency — the number clinicians look at first

Sleep efficiency is the percentage of your time in bed actually spent asleep:

Roughly 85–90%+ is considered healthy. Persistently lower suggests you are spending too much time in bed not sleeping — the exact problem CBT-I's sleep-restriction component targets. Only a diary can reveal this number, because it depends on times a sensor cannot know (when you tried to sleep, versus when you were reading in bed).

2. Which insomnia pattern you actually have

A fortnight of entries usually shows one of three shapes: long times to fall asleep (sleep-onset insomnia), repeated or prolonged night wakings (maintenance insomnia), or consistently waking long before your alarm (early-morning waking). They have different typical drivers — evening arousal and caffeine for the first, alcohol and stress for the second — so knowing your shape tells you where to aim.

3. The habits feeding the problem

This is where the factor column earns its keep. Set the bad nights beside the day's entries and correlations surface quickly: the 4 pm coffee (caffeine disrupts sleep even six hours before bed — Drake et al., 2013), the nightcap that fragments the second half of the night, the doomscrolling hour. Drift automates this step: log factors alongside each night and its sleep score breakdown shows which component — timing, consistency, duration or quality — is dragging you down.

4. That you may be sleeping more than you think

People with insomnia often substantially underestimate their sleep — lying awake for what feels like hours that a diary (or a partner) shows were 20 minutes. Seeing a written record of six-and-a-half real hours, night after night, is itself therapeutic for many people: it converts catastrophic "I never sleep" beliefs into a bounded, improvable problem. Challenging those beliefs is a core part of the cognitive side of CBT-I.

How diaries power CBT-I

CBT-I is the recommended first treatment for chronic insomnia — the NHS explicitly advises it ahead of long-term sleeping tablets, which are no longer routinely prescribed (NHS). Nearly every CBT-I technique consumes diary data:

• Sleep restriction/consolidation sets your allowed time in bed from your diary's average actual sleep, then expands it as efficiency improves — impossible without diary numbers.
• Stimulus control (bed is for sleep only; get up if awake ~20 minutes) is checked against diary-reported waking time.
• Cognitive work uses the diary as evidence against distorted beliefs about how little you sleep.

If you later use NHS services or a digital CBT-I programme, arriving with two weeks of diary data means treatment can start immediately rather than with a fortnight of baseline logging.

Paper or app?

Both work — the clinically important part is the morning habit, not the medium. An app has practical advantages: it prompts you, timestamps entries, computes efficiency, averages and trends automatically, and never gets left in a drawer. Drift also works without any wearable (see how to track sleep without a watch) and can pre-fill nights recorded by your iPhone via Apple Health, so the diary habit costs you seconds, not minutes.

Making the habit stick

The diary that helps is the one you actually keep, so remove every point of friction. Anchor the entry to something you already do every morning — kettle on, sit down, log the night. Keep it visible: a notebook on the breakfast table, or the app on your home screen with a morning reminder. And log the boring nights too; a diary of only the disasters tells you nothing about what your good nights have in common, and it is the good nights that hold the recipe. Finally, resist grading yourself day to day. The diary is a measuring instrument, not a scorecard — its value arrives at the end of the week, when you review the pattern, not each morning.

When a diary is not enough — see your GP

A sleep diary is a self-help and assessment tool, not a treatment for everything. Speak to your GP if your diary shows trouble sleeping at least three nights a week for three months or more, if daytime sleepiness is affecting your safety (especially driving), or if you have symptoms suggesting something beyond insomnia — loud snoring with gasping or choking (possible sleep apnoea), restless legs, or acting out dreams. Bring the diary: it is precisely what they will ask about (NHS — Insomnia).

Drift is a wellness tool, not a medical device, and this article is general information rather than medical advice. If you have persistent insomnia or any concerning sleep symptoms, please see your GP — the NHS insomnia guidance is a good starting point.