Sleep Calculator
Work out the best time to fall asleep or wake up using 90-minute sleep cycles — so your alarm lands between cycles and you wake up less groggy.
To wake up refreshed at 7:00 AM, fall asleep at one of these times:
Based on 90-minute sleep cycles plus about 15 minutes to fall asleep. Waking at the end of a cycle — rather than mid-cycle — helps you feel less groggy. Most adults do best on 5–6 cycles (7.5–9 hours). Cycle length varies by person, so treat these as a guide.
Setting an alarm and want to feel rested instead of foggy? Enter when you need to wake up and the calculator shows the bedtimes that end on a full sleep cycle. Everything is computed in your browser — nothing is saved.
How It Works
Pick a mode
Set your wake-up time, or your bedtime — or tap "going to bed now".
Read the cycle times
Each option ends on a 90-minute cycle boundary, plus time to fall asleep.
Aim for the highlighted one
6 cycles (about 9 hours) is the default best target for adults.
Frequently Asked Questions
How does a sleep cycle calculator work?+
Sleep runs in cycles of roughly 90 minutes, moving from light to deep to REM sleep. Waking at the end of a cycle feels easier than waking mid-cycle. The calculator counts backward or forward in 90-minute blocks (plus about 15 minutes to fall asleep) so your alarm lands between cycles.
What time should I go to bed to wake up at 7 AM?+
To wake at 7:00 AM, aim to fall asleep at about 9:45 PM (6 cycles), 11:15 PM (5 cycles), or 12:45 AM (4 cycles). Enter your own wake-up time above to get the exact bedtimes.
How many hours of sleep do I need?+
Most adults need 7–9 hours, which is 5 to 6 full sleep cycles. Teenagers generally need more. The calculator highlights the 6-cycle option as the best target for a typical adult.
Why do I wake up tired even after 8 hours?+
If your alarm goes off in the middle of a deep-sleep stage, you can feel groggy even after a full night — this is sleep inertia. Timing your wake-up to the end of a cycle helps avoid it.
Is a 90-minute sleep cycle exact?+
It is an average. Real cycles range from about 80 to 110 minutes and shift through the night, so treat the suggested times as a helpful guide rather than a precise rule.
When should I wake up if I go to sleep now?+
Tap "I'm going to bed now" and the calculator adds the time to fall asleep plus whole cycles, showing the wake-up times that end on a cycle boundary.