Sleep Calculator
Calculate optimal sleep and wake times
I need to wake up at:
💡 About Sleep Cycles
Each sleep cycle lasts about 90 minutes. Waking up between cycles helps you feel more refreshed. Adults typically need 5-6 complete cycles (7.5-9 hours) per night.
About Sleep Calculator
Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle, rather than in the middle of deep sleep, tends to feel considerably easier — this calculator works backwards or forwards from your chosen time to suggest which moments land on a cycle boundary.
How the times are worked out
The calculator counts in 90-minute blocks and adds about 15 minutes for the time it takes to fall asleep. If you need to be up at a fixed hour, it subtracts whole cycles from that hour; if you are going to bed now, it adds them. Five or six complete cycles — around seven and a half to nine hours — is the usual target for an adult.
How exact is the 90-minute figure?
It is an average, not a constant. Real cycles run from roughly 70 to 120 minutes, they lengthen through the night, and they differ between people and between nights. Treat the suggested times as sensible targets rather than precise instructions — being ten minutes off a theoretical boundary matters far less than total sleep and a consistent schedule.
What matters more than cycle timing
Regularity. Going to bed and waking at the same time every day, including weekends, does more for how rested you feel than optimising any single night. Consistent light exposure in the morning, avoiding caffeine within about eight hours of bed, and keeping the room dark and cool all outweigh cycle arithmetic. Persistent insomnia, loud snoring with pauses in breathing, or exhaustion despite adequate hours are worth raising with a doctor.