A simple daily log turns vague self-observations about mood into something a clinician can actually work with.
What to track
At minimum: a mood rating (a simple 1-10 scale or low/normal/high is enough), hours slept, and a quick note of anything unusually impulsive or unusually high-energy that day. Some people add medication adherence and any major life events, since those can help explain a spike or dip later.
Keep it short enough to actually do daily
A log that takes thirty seconds a day gets used. A log that takes ten minutes gets abandoned within a week. Most people do better with a short, consistent format than an elaborate one they only fill in occasionally.
How long before it's useful
Most clinicians find four to eight weeks of consistent daily tracking gives enough data to spot a real pattern, as opposed to normal day-to-day variation everyone experiences. Shorter stretches can still be worth bringing in, but the picture gets clearer with more consistent data.
Bring it to appointments
A written or app-based log is far more useful to a doctor or therapist than trying to recall mood shifts from memory during a short appointment. It can also help you and your clinician spot triggers, whether that's a change in sleep, a stressful period, or a medication adjustment, that might otherwise get missed.