Sleep Calculator
Find the ideal bedtime or wake-up time based on 90-minute sleep cycles. Waking at the end of a cycle — not in the middle — is what prevents that groggy feeling.
What do you want to calculate? 90-min cycles
When do you NEED to be awake? → Calculator shows best bedtimes
When are you planning to go to bed? → Calculator shows best wake-up times
Best times to go to bed if you need to wake up at 7:00 AM
One 90-minute sleep cycle (×4–6 cycles per night)
N1 Light
N2 Light
N3 Deep
REM
Brief wake
FAQs
Why do I wake up groggy even after 8 hours of sleep? ›
Grogginess is often caused by "sleep inertia" — waking up in the middle of a deep sleep (N3) stage rather than at a natural end-of-cycle transition. Sleep cycles last about 90 minutes. If you sleep exactly 8 hours but your alarm interrupts a deep sleep cycle at the 7.5-hour mark, you'll feel worse than if you'd slept 7.5 hours and woken at a natural cycle end. This calculator shows you times to aim for that align with 90-minute cycle boundaries.
How many hours of sleep do adults need? ›
The CDC and American Academy of Sleep Medicine recommend 7–9 hours for adults 18–60. Teens (13–18) need 8–10 hours; school-age children (6–12) need 9–12 hours; adults 65+ need 7–8 hours. About 1 in 3 US adults don't get enough sleep. Most people do best with 5–6 complete 90-minute cycles (7.5 or 9 hours) plus sleep onset time.