Sleep Cycle Bedtime Calculator: When to Go to Bed (or Wake Up)
Find the bedtime that lets you wake at the end of a sleep cycle, or the best alarm times if you go to bed now. Uses 90-minute cycles, your time to fall asleep and the CDC sleep hours for your age.
How it works
Bedtime = wake-up time − (cycles × cycle length + time to fall asleep) · Wake-up time = bedtime + time to fall asleep + cycles × cycle length
Sleep runs in cycles of roughly 90 minutes, moving from light sleep through deep sleep and into REM before the next cycle begins. Waking at the end of a cycle, when sleep is light, usually feels less groggy than being woken out of deep sleep. Choose whether you know your wake-up time or your bedtime. The calculator counts whole cycles back from the alarm (or forward from bedtime) and adds the minutes you usually need to fall asleep, so the last cycle ends at the alarm. It then suggests the fewest whole cycles that meet the CDC recommendation for your age: 7 or more hours for adults aged 18 to 60, 7 to 9 hours at 61 to 64, 7 to 8 hours from 65, 8 to 10 hours for teens and 9 to 12 hours for children aged 6 to 12. With 90-minute cycles that is 5 cycles (7.5 hours) for most adults and 6 cycles (9 hours) for teens. The table lists 3 to 7 cycles so you can trade sleep for an earlier or later time. Cycle length differs between people and nights, so you can change it under More options, and the results are targets rather than exact alarms.
Worked example
Default: wake at 07:00, 14 minutes to fall asleep, age 18 to 60, 90-minute cycles. Adults need 7 or more hours, and 5 cycles × 90 = 450 minutes (7 h 30 min) is the fewest whole cycles that reaches it. Time in bed = 450 + 14 = 464 minutes (7 h 44 min), so the suggested bedtime is 7:00 AM − 7 h 44 min = 11:16 PM, falling asleep at 11:30 PM. Six cycles (9 hours) would mean bed at 9:46 PM, and four cycles (6 hours) at 12:46 AM. In "Go to bed at" mode, getting into bed at 23:00 means falling asleep at 11:14 PM and a suggested alarm of 6:44 AM.
Sources: CDC: About sleep (recommended hours by age) · Sleep Foundation: Sleep calculator · Calculator.net: Sleep calculator
Frequently asked questions
What time should I go to bed to wake up at 7 AM?
With 90-minute cycles and about 14 minutes to fall asleep, aim for 11:16 PM (5 cycles, 7.5 hours of sleep) or 9:46 PM (6 cycles, 9 hours). If you fall asleep faster or slower, the bedtime moves by the same number of minutes.
Is every sleep cycle exactly 90 minutes?
No. Cycles average about 90 minutes but range from roughly 70 to 120 minutes, and REM periods get longer toward morning. Use the More options field to set your own cycle length if you know it, and treat the times as close targets.
How many sleep cycles do I need?
Most adults need 7 or more hours a night, which is 5 cycles (7.5 hours) with 90-minute cycles. Teens need 8 to 10 hours (about 6 cycles) and children aged 6 to 12 need 9 to 12 hours, according to the CDC.
Why add time to fall asleep?
Cycles only start once you are asleep. Adding your usual sleep-onset time, often 10 to 20 minutes, means the count lands the end of your last cycle at the alarm instead of before it.
Is it better to sleep 6 hours or 7.5 hours?
More total sleep matters more than waking at a cycle boundary. Six hours (4 cycles) may feel easier to wake from than 7 hours, but it is below the 7 hours adults need, so use it only occasionally.
Related calculators
Educational estimate, not medical advice. Ongoing trouble falling or staying asleep, loud snoring or daytime sleepiness are worth discussing with a doctor.