Melatonin Timing Calculator
Find your ideal melatonin dose and when to take it based on your weight, age, and sleep issue. Useful for shift workers, older adults, and anyone struggling to reset their sleep schedule.
About this calculator
Melatonin is a hormone your brain naturally releases as darkness approaches, signaling that it's time to sleep. Supplemental melatonin can help shift your sleep timing or compensate for reduced natural production. The dosage formula used here is: dose (mg) = clamp(0.5–10, (bodyWeight / 70) × (age > 55 ? 3 : 1) + (shift_work ? 2 : 0)). Older adults (over 55) often produce less melatonin naturally, so the formula triples the base dose relative to body weight. Shift workers receive an additional 2 mg to help overcome strong circadian disruption. The result is clamped between 0.5 mg and 10 mg to stay within evidence-based safe ranges. Timing matters as much as dose — melatonin is most effective when taken 30–60 minutes before your target bedtime.
How to use
Example: A 35-year-old person weighing 84 kg with jet lag (not shift work) wants to move bedtime earlier. Step 1 — base dose: (84 / 70) × 1 = 1.2 mg. Step 2 — shift-work adjustment: not applicable, so add 0. Step 3 — clamp: 1.2 is between 0.5 and 10, so the recommended dose is 1.2 mg. Step 4 — timing: if target bedtime is 10:30 PM, take melatonin at approximately 9:45–10:00 PM. Enter your own weight, age, target bedtime, and current average bedtime to get your personalised recommendation.
Frequently asked questions
How long before bed should I take melatonin for it to be effective?
Melatonin typically takes 30 to 60 minutes to reach peak concentration in the blood, so taking it roughly 30–60 minutes before your target bedtime is ideal. Taking it too early can cause drowsiness at the wrong time, while taking it too late reduces its circadian-shifting effect. For gradually shifting a delayed sleep schedule, some research suggests taking it even earlier — up to 5–6 hours before desired sleep onset — at a very low dose (0.5 mg). Always start with the lowest effective dose and adjust based on your response.
What melatonin dose is safe for adults over 55?
Adults over 55 naturally produce significantly less melatonin, which is one reason sleep problems become more common with age. Research suggests that older adults may benefit from slightly higher doses, typically in the 1–3 mg range, compared to the 0.5–1 mg that is often sufficient for younger adults. This calculator reflects that by applying a 3× age multiplier for users over 55. However, even for older adults, it is advisable to start low (0.5–1 mg) and increase only if needed, as higher doses can cause next-day grogginess.
Does melatonin work differently for shift workers than for regular sleepers?
Yes — shift workers face ongoing circadian misalignment because their required sleep times conflict with their body's natural light-dark cycle. Melatonin can help signal sleep at unconventional hours, but shift workers generally need a somewhat higher dose and careful timing relative to their specific shift rotation. This calculator adds 2 mg for shift workers to account for stronger circadian resistance. Consistency is critical: taking melatonin at the same clock time each day you need to sleep helps re-anchor your internal clock more effectively than sporadic use.