Newborns (0–3 months) need 14–17 hours, infants (4–11 months) 12–15, toddlers (1–2 years) 11–14, preschoolers (3–5) 10–13, school-age children (6–13) 9–11, teenagers (14–17) 8–10, adults (18–64) 7–9, and older adults (65+) 7–8 hours.

Teenagers need 8–10 hours, which is about 5–7 sleep cycles. Many fall short on school nights, so an earlier, consistent bedtime helps. Use the bedtime calculator with the school wake-up time to find the right time to sleep.

Sleep supports rapid brain development, growth-hormone release, memory consolidation and immune function — all of which are most intense in early life, so younger children need far more total sleep than adults.

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.