Sleep Calculator — Best Bedtime & Wake-Up Times
Waking in the middle of a deep sleep cycle leaves you groggy even after 8 hours; waking between cycles feels refreshed even after less. Sleep runs in roughly 90-minute cycles. Tell the calculator when you must wake up (or when you're going to bed) and it suggests the times that align with complete cycles.
Cycle length varies person to person (80–100 min); use these as a helpful guide and notice what leaves you freshest.
General wellness information, not medical advice. Persistent sleep problems deserve a doctor's attention.
How to use this tool
- Choose whether you're setting a wake-up time or a bedtime.
- Pick the time, and how long you usually take to fall asleep.
- Press the button — the highlighted 'recommended' options give a full 7.5 hours across 5 cycles.
Frequently asked questions
Why does waking between sleep cycles matter?
Each ~90-minute cycle moves from light to deep to REM sleep. Being woken during deep sleep causes 'sleep inertia' — grogginess that can last 30+ minutes. Waking at the end of a cycle, in lighter sleep, feels far more refreshing, even with slightly less total sleep.
How many hours of sleep do I actually need?
Most adults need 7–9 hours (5–6 cycles). Teens need more, older adults sometimes slightly less. Quality matters as much as quantity — consistent timing and uninterrupted cycles beat long but broken sleep.
Is the 90-minute cycle exact?
It's an average; real cycles range 80–100 minutes and lengthen through the night. That's why these are guidelines, not guarantees. Try the suggested times for a week and notice which leaves you sharpest — then personalise.
What helps me fall asleep faster?
Consistency (same bedtime daily), no screens 30–60 minutes before bed, a cool dark room, and avoiding caffeine after early afternoon. If you routinely take over 30 minutes to fall asleep, set the buffer higher so the maths reflects reality.
Should I use this for shift work or jet lag?
The cycle logic still helps, but shift work and jet lag also disrupt your body clock (circadian rhythm). Aligning cycles is one piece; gradual schedule shifts and light exposure matter too for those situations.