Free sleep calculator
Sleep Cycle Calculator
Wake up between sleep cycles, not in the middle of one. Pick a time and get your options.
Bedtimes below already include ~15 minutes to fall asleep.
Not medical advice. This tool gives a general estimate for informational purposes only — it does not replace professional judgment. If you're concerned, contact a doctor right away. This is sleep-cycle arithmetic based on population averages, not a clinical measurement of your own cycles — real cycles vary by person and night. If you regularly struggle to fall asleep, stay asleep, or feel unrested, talk to a doctor or sleep specialist.
How this works & sources
Sleep runs in cycles of roughly 90 minutes, each moving from light sleep down into deep sleep and REM and back toward light sleep. Waking at the end of a cycle — in light sleep — tends to feel easier than being pulled out of deep sleep mid-cycle. This calculator counts back (or forward) in 90-minute blocks and adds about 15 minutes to fall asleep, so each suggested time lands on a cycle boundary.
The 90-minute cycle length and the "four to six sleep cycles" in a typical night come from the Sleep Foundation's "Stages of Sleep"; the National Sleep Foundation gives the same 90-minute figure. The ~15 minutes added to fall asleep is the middle of Sleep Foundation's normal sleep latency for a healthy adult — "between 10 and 20 minutes." And the 5–6 cycles flagged as recommended (7.5–9 hours) are the part of the National Sleep Foundation's 7–9 hour adult recommendation that lands on a whole cycle.
One honest caveat: cycle length isn't exactly 90 minutes for everyone, and it shifts across the night and with age, alcohol, and recent sleep. Treat these as helpful targets, not a precise readout of your own sleep — and prioritise getting enough total sleep over hitting an exact cycle boundary.