Melatonin Onset Timing Calculator

How it is calculated

Enter your usual bedtime as 24-hour HH:MM (the hour may be one or two digits) and pick a goal. The tool first estimates your dim-light melatonin onset (DLMO), the point where your body starts producing melatonin, as DLMO = bedtime − 120 min. For falling asleep faster it returns a time 60 min before bedtime. For shifting your clock earlier it returns bedtime − 300 min, which is 3 hours before the estimated DLMO. If the goal is left out, sleep onset is used. Times wrap past midnight. A bedtime that is not written as HH:MM, or an unknown goal, gives no result. The 2-hour DLMO gap is an average assumption, and real onset differs between people. This is a timing aid, not medical advice or a dose recommendation.

Common mistakes

• Entering the time you wake up or the time you start winding down instead of the time you actually go to sleep. Every result is counted back from the bedtime you type.
• Typing 12-hour times such as 11:30 PM. Only the 24-hour HH:MM form works, so use 23:30; the 12-hour form gives no result.
• Using the phase-advance time as a sleep aid. It is several hours before bed and meant to move the body clock, not to make you drowsy right away.
• Treating the DLMO line as a measured value. It is simply bedtime minus 2 hours; a true DLMO needs saliva or blood sampling in dim light.
• Changing bedtime on the day without changing the goal. The two goals give very different times, so check the selected purpose.