What Time Should I Go to Bed?
Tell the calculator when you need to wake up, and it works backwards through 90-minute sleep cycles (plus 15 minutes to fall asleep) to show the best times to go to bed. Pick the bedtime that gives you 5–6 full cycles to wake up at the end of a cycle rather than in the middle of one.
Choose your mode, enter a time, and press Calculate to find optimal sleep times.
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Frequently asked questions
What time should I go to bed to wake up at 6 AM?+
To wake at 6:00 AM feeling rested, aim to be asleep by about 9:00 PM (6 cycles) or 10:30 PM (5 cycles). Allowing ~15 minutes to fall asleep, that means getting into bed around 8:45 PM or 10:15 PM. Enter 6:00 above for your exact options.
Is it better to sleep more cycles or wake at a fixed time?+
Aim for 5–6 complete cycles AND a consistent wake time. If you can't get 6 cycles, waking at the end of 5 cycles usually feels better than squeezing in extra time that ends mid-cycle.
How does the sleep calculator work?+
Sleep happens in roughly 90-minute cycles. Waking at the end of a cycle feels easier than being pulled out of one mid-way. The calculator takes your wake-up time (or bedtime), adds the ~15 minutes most people take to fall asleep, and counts whole 90-minute cycles to suggest the best times to sleep or wake.
How many hours of sleep do I need?+
Most adults need 7–9 hours — about 5 to 6 complete sleep cycles per night. Teenagers need 8–10 hours, school-age children 9–11, and younger children and babies more. Older adults often need slightly less, around 7–8 hours.
Why do I wake up tired even after 8 hours?+
Waking in the middle of a deep-sleep stage leaves you groggy (sleep inertia) even after a full night. Aligning your alarm to the end of a 90-minute cycle — what this calculator does — helps you wake more refreshed. Consistent sleep and wake times matter just as much.
Is the sleep calculator a medical tool?+
No — it's a general planning guide based on average 90-minute cycles, and individual cycles vary. If you have ongoing insomnia, loud snoring, daytime sleepiness, or chronic fatigue, speak to a doctor, as these can signal a treatable sleep disorder.