Sleep Calculator

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.

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.

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.

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.