Bedtime calculator
What time should you go to bed to wake up at a specific time? Enter your target wake time below. The calculator works backwards through 90-minute sleep cycles and adds ~14 minutes to fall asleep — so you can wake at the end of a cycle and avoid grogginess.
Go to bed at one of these times
includes ~14 min to fall asleepFull restorative sleep
Recommended for most adults
Acceptable on short nights
Minimum — expect grogginess
Pick a time at the start of a complete cycle to wake feeling rested, not groggy.
How to use the bedtime calculator
Set the alarm clock you actually have to set tomorrow. The calculator returns four bedtimes — one for each of 3, 4, 5, or 6 full sleep cycles. Pick the latest one that still gives you at least 5 cycles. Below 5 cycles, you’re running a sleep deficit that compounds across the week.
Why cycles, not hours
Sleep runs in roughly 90-minute cycles: light sleep, then deep slow-wave sleep, then REM, then back to light (NIH overview of sleep stages). Waking during deep sleep produces sleep inertia— the dull, slow, groggy feeling that takes 30+ minutes to fade. Waking at the end of a cycle, in light sleep, feels almost effortless. That’s why two people sleeping the same number of hours can feel very differently rested.
The 90-minute number is a population average. Real cycles range from about 80 to 110 minutes and tend to lengthen across the night (more REM, less deep sleep in the final cycles). The calculator can’t know your personal cycle length, but the average gets most adults to within 10–15 minutes of optimal — far better than picking a bedtime at random.
What about the 14 minutes to fall asleep?
Healthy adults take 10 to 20 minutes to fall asleep — sleep researchers call this sleep latency. We use 14 minutes as a midpoint. If you usually fall asleep in under 10 minutes you may be sleep-deprived; if it routinely takes you over 30, that’s a sign of insomnia worth taking seriously.
If you keep waking up tired
Try shifting bedtime in 15-minute increments for a week each. If 11:06 PM leaves you groggy, try 10:51 PM and 11:21 PM and see which feels better. Your personal cycle length is likely off the 90-minute average by 5–10 minutes in one direction.
Other common culprits: caffeine too late, alcohol within 3 hours of bed (suppresses REM), bedroom too warm (the body needs to drop ~1°C to enter deep sleep), light exposure within an hour of bed.
Frequently asked questions
What time should I go to bed to wake up at 6 AM?
For 6 cycles (9 hours of sleep), bed at 8:36 PM. For 5 cycles (7.5 hours), bed at 10:06 PM. For 4 cycles (6 hours), bed at 11:36 PM. Each adds the ~14 minutes most adults need to fall asleep, so the actual go-to-bed time is right when you turn off the light.
What time should I go to bed to wake up at 7 AM?
For 6 cycles, bed at 9:36 PM. For 5 cycles, bed at 11:06 PM. For 4 cycles, bed at 12:36 AM. Use the calculator above with 07:00 as your wake time to see all options.
Is going to bed at the same time every night that important?
Yes — consistency is one of the single strongest predictors of sleep quality. A regular bedtime trains your circadian rhythm so falling asleep happens faster and deep sleep stages are longer. Aim to stay within a 30-minute window on weeknights, even weekends if you can.
What if I can’t fall asleep within 20 minutes?
Get out of bed. Read a paper book in dim light in another room until you feel sleepy, then return to bed. This breaks the "lying in bed awake" association that turns occasional insomnia into chronic. If this keeps happening for more than three weeks, consider seeing a sleep doctor — chronic insomnia responds well to CBT-I.
How is this different from a "hours of sleep" calculator?
A hours-of-sleep calculator just subtracts 8 hours from your wake time. This one targets the *end* of a complete 90-minute cycle, so you wake during light sleep rather than mid-deep-sleep. Same total time can feel dramatically different depending on which stage you’re in when the alarm goes off.
Does this account for sleep stages changing through the night?
Approximately. Cycles average 90 minutes but actually get longer through the night (more REM, less deep sleep), so the last cycle can run 100–110 minutes. For most people the 90-minute model is close enough — if you wake groggy at a recommended time, try going to bed 10 minutes earlier next time.
Common wake times
Specific bedtimes for the most-asked wake times: