Find bedtimes that let you wake at the end of a 90-minute sleep cycle, for 4, 5 or 6 cycles.
Result
How to use this tool
Enter the time you need to wake up.
Enter how long you usually take to fall asleep.
Read bedtimes for 4, 5 and 6 full cycles.
Pick the bedtime that gives you enough total sleep.
Formula & worked example
Waking at 07:00 with 14 minutes to fall asleep gives 5-cycle bedtime 07:00 minus 450 minus 14 minutes = 23:16.
Limitations — read this before you rely on it
Cycle length varies between people and across the night; the 90-minute figure is an average. This is a scheduling aid, not a sleep-disorder assessment. This tool is for education only and is not medical advice. Talk to a clinician about any result that worries you, and never change treatment because of a calculator result.
Frequently asked questions
Sleep runs in roughly 90-minute cycles through light, deep and REM stages, though individual cycles vary.
Five cycles, about 7.5 hours plus falling-asleep time, suits most adults; six cycles suits longer sleepers.
You may feel groggier, known as sleep inertia; it usually passes within minutes.
No. Persistent trouble sleeping deserves a clinician, not a bedtime calculator.
Yes in reverse: add whole 90-minute cycles to your bedtime to find good wake times.