Sleep Calculator — When Should I Go to Bed?
This sleep calculator finds the best times to fall asleep and wake up based on 90-minute sleep cycles. Pick the time you need to wake up and it suggests bedtimes that let you finish a complete cycle, or enter your bedtime (or use the current time) to see the best wake-up times. Waking at the end of a cycle, instead of in the middle of one, makes mornings feel far less groggy.
The time your alarm goes off.
How Sleep Cycles Work
Sleep is not one continuous state. Through the night your brain moves through repeating cycles of roughly 90 minutes, each passing from light sleep into deep sleep and finally into REM sleep, the stage where most vivid dreaming happens. Light sleep eases you in, deep sleep does the heavy lifting of physical repair, and REM sleep supports memory and mood. A typical night strings together five or six of these cycles back to back.
The stage you are in when the alarm goes off matters as much as how long you slept. Wake in the middle of deep sleep and you get sleep inertia: that heavy, disoriented grogginess that can linger for a long time after waking. Wake at the end of a cycle, when sleep is at its lightest, and getting up feels much easier. This calculator works backward from your wake-up time (or forward from your bedtime) in 90-minute steps, then adds the average 15 minutes it takes to fall asleep, so your alarm lands at the end of a cycle rather than the middle of one.
How Much Sleep Do You Need?
Sleep needs change with age. Babies and young children need far more sleep than adults because so much growth and brain development happens overnight, while most adults settle into a steady 7 to 9 hours. The ranges below follow the National Sleep Foundation's recommendations. They are ranges for a reason: some people genuinely thrive at the low end while others need the high end, so use how you feel during the day as the real test.
| Age group | Age | Recommended sleep |
|---|---|---|
| Newborn | 0-3 months | 14-17 hours |
| Infant | 4-11 months | 12-15 hours |
| Toddler | 1-2 years | 11-14 hours |
| Preschool | 3-5 years | 10-13 hours |
| School age | 6-13 years | 9-11 hours |
| Teen | 14-17 years | 8-10 hours |
| Adult | 18-64 years | 7-9 hours |
| Older adult | 65+ years | 7-8 hours |
For adults, 7 to 9 hours lines up neatly with 5 to 6 complete sleep cycles, which is why the calculator marks those rows as recommended. Consistently sleeping less than 7 hours is linked to poorer concentration, mood, and long-term health, even if you feel like you have adapted to it. Curious exactly how long you slept last night? Try our time duration calculator to count the hours and minutes between any two times.
This calculator offers general guidance on sleep timing and is not medical advice; talk to a doctor about persistent sleep problems.
Tips for Better Sleep
Good sleep starts long before your head hits the pillow. The single most effective habit is a consistent schedule: going to bed and waking up at the same times every day, weekends included, keeps your body clock aligned so you get sleepy and wake up on cue. Bright light helps set that clock too. Get outside or near a sunny window early in the day, and dim the lights in the evening as bedtime approaches.
Watch your caffeine cutoff: caffeine lingers in the body for hours, so a coffee in the late afternoon can still be working against you at midnight. Aim to stop at least 6 to 8 hours before bed. Put screens away in the last hour, since both the light and the stimulation make it harder to wind down. Finally, set the room up for sleep: cool, dark, and quiet. Around 65 degrees Fahrenheit (18 degrees Celsius) suits most people, and blackout curtains or a sleep mask handle stray light. Pair those habits with cycle-timed alarms from the calculator above and mornings get noticeably easier.
Frequently Asked Questions
Most adults do best with 5 to 6 complete sleep cycles per night. At about 90 minutes each, that works out to 7.5 to 9 hours of sleep, which matches the 7 to 9 hours recommended for adults. Four cycles (6 hours) can work occasionally, but it is below the recommended range for most people.
For most adults, no. Six hours is 4 complete sleep cycles, which is below the recommended 7 to 9 hours. You may feel relatively alert because you wake at the end of a cycle, but regularly sleeping 6 hours or less is linked to reduced focus, mood, and long-term health. Treat it as a fallback for a short night, not a routine.
You probably woke in the middle of a sleep cycle, most likely during deep sleep. That heavy, disoriented feeling is called sleep inertia, and it can happen even after 8 or more hours if your alarm lands mid-cycle. Timing your alarm for the end of a 90-minute cycle, as this calculator does, makes waking feel easier.
To wake at 6:00 AM, go to bed at 8:45 PM for 6 cycles (9 hours of sleep) or 10:15 PM for 5 cycles (7.5 hours). If those are not possible, 11:45 PM gives 4 cycles (6 hours). These times include the average 15 minutes it takes to fall asleep.
On average, yes. Most healthy adults take about 10 to 20 minutes to fall asleep, so this calculator uses 15 minutes. If you reliably drop off faster or slower, shift the suggested times by the difference. Regularly falling asleep in under 5 minutes can be a sign of sleep deprivation, while routinely taking much longer than 30 minutes may be worth discussing with a doctor.