How to keep a sleep diary

Fill it in every morning, within an hour of getting up, for two weeks. Write down when you went to bed, how long it took to fall asleep, how often you woke and for how long, when you woke for good, when you got up, and how well you slept.

What to write down

Sleep researchers agreed a standard form in 2012, the Consensus Sleep Diary. Its core questions, and the sleep log in the American Academy of Sleep Medicine's insomnia guideline, cover the same ground:

• the time you went to bed, and the time you tried to go to sleep
• how long it took to fall asleep
• how many times you woke, and how long you were awake in total
• the time you woke for the last time, and the time you got out of bed
• how well you slept

The guideline adds that a log can also record how you felt during the day, medicines, caffeine and alcohol. Those are what let you look for causes later, so it's worth a line for each.

When to fill it in

Once, in the morning. The Consensus Sleep Diary asks for every item to be completed within an hour of getting out of bed, and an NHS trust's advice for families says the same. Keep the diary by your bed or on your phone so it's the first thing you do.

Don't check the clock in the night to get exact times. A best guess in the morning is what a sleep diary is designed for: it records your night as you experienced it.

How long to keep it

Two weeks. The AASM guideline asks for a two-week sleep log, ideally before the first appointment, so the doctor sees a pattern rather than one bad night. If you're having treatment, keep going: the same guideline says diary data should be collected before and during treatment.

Mistakes that make a diary less useful

• Filling in several days at once. Memory blurs quickly. If you miss a night, leave it blank.
• Measuring from bedtime to sleep. Time to fall asleep starts when you tried to sleep. Reading in bed first is part of time in bed, but not of the time it took to fall asleep.
• Skipping the good nights. They're what you compare the bad ones with.
• Leaving out the day before. Coffee, drinks, exercise and stress belong to the night that followed.

Paper, online or an app

Any of them works if you fill it in every morning. A printable sleep diary is easy to hand to a doctor. The online sleep diary works out your sleep efficiency each night. An app can remind you and keep months of nights.

This guide isn't medical advice. If poor sleep has gone on for months or makes the day hard to cope with, see your doctor.