Sleep Cycle Calculator
Pick a wake-up time and get candidate bedtimes at 4–6 cycles of the conventional 90 minutes — or flip the mode to turn a bedtime into wake times. The fall-asleep buffer is yours to edit. Recovery pairs with training load: the TDEE Calculator and heart-rate zones cover the daytime side.
Plan around your cycles
Example: wake at 7:00 AM, 5 cycles + 15 min to fall asleep → in bed by 11:15 PM.
The arithmetic behind the clock times
Each option is (cycles × 90 minutes) of sleep plus your fall-asleep buffer, counted back from the wake time (or forward from the bedtime), wrapping across midnight when needed. For a 7:00 AM alarm, five cycles plus the default 15-minute buffer means getting into bed at 11:15 PM for 7 h 30 min of sleep — computed by the same tested engine as the calculator. No science fits a wall clock this neatly, which is why the page shows three options rather than declaring one perfect bedtime.
Where the 90-minute figure comes from — and where it breaks
Sleep researchers describe adult cycles as averaging roughly 90 minutes, but the measured spread runs about 70–110 minutes, and early-night cycles carry more deep sleep than the REM-heavy ones before dawn. A planner built on the average can be a useful scaffold for a consistent schedule — consistency itself being the intervention with the best evidence — but it cannot know where your cycles actually fall on a given night. If an option leaves you consistently groggy, shift it by 15–20 minutes and let your mornings vote.
Frequently asked questions
Why plan sleep in 90-minute cycles?
A night of sleep moves through repeating stages — light sleep, deep sleep, and REM — and one pass through the sequence averages about 90 minutes in adults. Timing the alarm near a cycle boundary aims to avoid waking from the deepest stage, when grogginess (sleep inertia) tends to be worst.
Is everyone’s cycle exactly 90 minutes?
No — that is this calculator’s most important caveat. Measured cycles typically run about 70 to 110 minutes, differ between people, and change in length across the same night. The 90-minute figure is a population average used for planning, so treat the computed times as starting points to adjust by feel.
What does the fall-asleep buffer do?
Cycles are counted from when you fall asleep, not from lights out. The buffer (default 15 minutes, editable from 0 to 120) shifts the in-bed time to allow for drifting off. If you routinely fall asleep much faster or slower, set it to match — it changes every listed time one for one.
How many cycles should I aim for?
Five cycles is 7 h 30 min of sleep and six is 9 h, which brackets the seven-or-more hours per night commonly recommended for adults. Four cycles (6 h) is listed as a fallback for short nights, not a target to plan around.
What if I still wake up groggy at a "good" time?
Some sleep inertia after waking is normal, and cycle arithmetic cannot eliminate it. Persistently unrefreshing sleep, loud snoring, or heavy daytime sleepiness are reasons to talk to a clinician — this planner arranges clock times and makes no claims about sleep disorders.
Not medical advice: this planner does calendar arithmetic on a population-average cycle length; it does not assess sleep quality or sleep disorders. Persistent sleep problems are a matter for a qualified clinician. Data is processed locally in your browser and never transmitted. See the methodology page.