A sleep diary is a self-monitoring tool used to systematically track and record information about a person’s sleep over time. It is one of the simplest and most effective ways to gain insight into sleep patterns, identify factors affecting sleep quality, and monitor progress during treatment for sleep problems. A typical sleep diary records information such as the time of going to bed, the time of falling asleep (estimated), the number and duration of awakenings during the night, the time of final waking, the total hours of sleep, any daytime naps, consumption of caffeine or alcohol, exercise, stress levels, and an overall rating of sleep quality and daytime alertness. Sleep diaries are widely used in the assessment and treatment of insomnia and other sleep disorders. Before beginning treatment such as cognitive behavioral therapy for insomnia (CBT-I), a sleep diary is typically kept for one to two weeks to establish a baseline picture of the person’s sleep. The data gathered helps the therapist or doctor identify problematic patterns and tailor treatment accordingly. During treatment, ongoing diary entries allow progress to be tracked and adjustments to be made. Sleep diaries can also be valuable as a personal tool for anyone who wants to better understand their sleep. By reviewing patterns over several weeks, you may notice connections between lifestyle factors — such as late-night caffeine, irregular bedtimes, or stressful days — and sleep quality. Keeping a sleep diary is straightforward and requires only a few minutes each morning. It can be done with a simple pen-and-paper format or using a dedicated sleep app.