Sleep Calculator
Bedtimes and wake times aligned to sleep cycles.
24-hour clock. 7 means 07:00, 23 means 23:00.
Bedtime for six full cycles
21:45
waking at 07:00
The 90-minute cycle is an average — real cycles run 70 to 120 minutes, so treat the alignment as approximate. Total sleep and a consistent schedule matter more.
How the Sleep Calculator works
Sleep runs in cycles of roughly 90 minutes, moving from light through deep sleep and into REM. Waking at the end of a cycle generally feels better than being pulled out of deep sleep partway through, which is where grogginess comes from.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, but genuinely variable — 70 to 120 minutes between individuals, and even between cycles in one night. Early cycles carry more deep sleep, later ones more REM, so they are not interchangeable.
How many sleep cycles do I need?
Five to six, which is 7.5 to 9 hours. Most adults need 7-9 hours total. Regularly getting five or fewer cycles accumulates a sleep debt that weekend catch-up only partly repays.
Does waking between cycles really help?
There is reasonable evidence that waking from light sleep reduces sleep inertia — the groggy period after waking. But the 90-minute figure is an average, so the alignment is approximate. Total sleep and a consistent schedule matter more.
How long does it take to fall asleep?
10 to 20 minutes is typical and healthy, which is why this calculator adds 15 minutes to bedtime estimates. Falling asleep in under five minutes consistently is a sign of significant sleep deprivation, not efficiency.