CircadianHub
🌙 CircadianHub
Pick when you need to wake up and we'll suggest bedtimes.
☀️ Wake-Up Calculator
Pick when you're going to bed and we'll suggest wake-up times.
⏰ Nap Planner
Choose a nap type to see how long to sleep and when you'll wake.
🏥 Shift Worker Mode
For nurses, doctors, first responders and factory workers.
A sleep cycle lasts about 90 minutes, moving through light, deep and REM sleep. Waking at the end of a cycle instead of the middle of one helps you feel more refreshed, which is why timing your sleep matters as much as its length.
How the sleep calculator works
CircadianHub turns one time you know, such as when you must get up, into a short list of sleep times that fit the way sleep is organised. The tabs above cover four situations: choosing a bedtime for a fixed wake-up time, choosing a wake-up time for a fixed bedtime, planning a nap, and scheduling sleep around a night or rotating shift.
Sleep happens in cycles of about 90 minutes
Through the night you move through light sleep, deep sleep and REM sleep, then start again. One loop takes about 90 minutes on average, though it can be anywhere from roughly 70 to 110 minutes and varies from night to night. The calculator counts back from your wake-up time in 90-minute steps, so each suggested bedtime gives you a whole number of cycles. Five cycles is 7.5 hours and six is 9 hours, which is why those totals are marked as recommended for most adults. Read more in how 90-minute sleep cycles work.
Why the fall-asleep time is added
The time it takes to fall asleep is called sleep latency. The calculator adds 14 minutes by default and lets you allow for longer. If you fall asleep in a minute or two almost every night, that can be a sign you are short on sleep; if it regularly takes much longer than 30 minutes, see what sleep latency means and our tips on falling asleep faster.
Waking mid-cycle and sleep inertia
Waking from deep sleep tends to leave you groggy, a state called sleep inertia, with slower thinking and a pull to go back to sleep. It usually fades within 15 to 30 minutes. Aiming for the end of a cycle can reduce it, but total sleep matters more than exact timing, and cycles are not identical every night. The evidence is explained in does waking mid-cycle make you groggy?.
Your body clock sets the rhythm
Alongside sleep cycles you have a circadian rhythm, an internal clock of about 24 hours that is set mainly by light. It controls when you feel sleepy, when body temperature falls and when melatonin rises. People differ in whether they naturally lean early or late (see chronotypes), and a steady wake-up time with morning daylight is the simplest way to keep the clock stable. Shift work and travel across time zones pull it out of line, which is what the Shift Worker mode and the Jet Lag Planner help you plan for.
How much sleep do you need?
Most adults do best with seven to nine hours, with teenagers and children needing more. Use the calculator as a starting point, then adjust by 15 to 30 minutes based on how you feel after a week. Our guide to how much sleep you need lists the ranges by age. The results are estimates and general information, not medical advice.