Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles. Wake up refreshed at natural cycle boundaries.
Recommended bedtimes (best first)
6 cycles / 9h sleep time
5 cycles / 7h 30m sleep time
4 cycles / 6h sleep time
3 cycles / 4h 30m sleep time
2 cycles / 3h sleep time
1 cycle = 90 min (light → deep → REM sleep)
Individual sleep needs vary. Use this as a general guideline.
How to Use
Select a mode
Choose 'Wake-up → Bedtime' to find when to go to sleep, or 'Bedtime → Wake-up' to find the best times to wake up.
Enter your time and fall-asleep delay
Enter your planned wake-up or bedtime. Adjust the 'time to fall asleep' to match how long it typically takes you to drift off after getting into bed.
View recommended times
Times are calculated to align with the end of a 90-minute sleep cycle, when waking up is easiest. More cycles mean more sleep.
FAQ
A sleep cycle lasts about 90 minutes and consists of light sleep (non-REM), deep sleep, and REM sleep. Waking up near the end of a cycle — during lighter sleep — is generally easier and leaves you feeling more refreshed.
Most adults do best with 5–6 cycles (about 7.5–9 hours). Some people function well on 4 cycles (6 hours), but chronic sleep deprivation is linked to serious health risks.
The average healthy adult falls asleep in 10–20 minutes. Falling asleep in under 5 minutes may indicate sleep debt, while taking more than 30 minutes regularly could suggest insomnia.
Waking during deep sleep (non-REM stage 3) causes 'sleep inertia' — intense grogginess and disorientation that can last 30–60 minutes. Timing your alarm to the end of a cycle reduces this effect.