Enter your wake-up time and get the exact bedtimes that end a 90-minute sleep cycle: 4, 5 or 6 cycles, with 15 minutes already added for falling asleep.
| Input | Result |
|---|---|
| Wake at 6:00 AM | Bed at 8:45 PM / 10:15 PM / 11:45 PM / 1:15 AM |
| Wake at 7:00 AM | Bed at 9:45 PM / 11:15 PM / 12:45 AM / 2:15 AM |
| Wake at 8:00 AM | Bed at 10:45 PM / 12:15 AM / 1:45 AM / 3:15 AM |
| Age group | Recommended sleep |
|---|---|
| Adult (18-60 years) | 7 or more hours |
| Older adult (65+) | 7-8 hours |
| Teen (13-17 years) | 8-10 hours |
| School age (6-12 years) | 9-12 hours |
| Preschool (3-5 years) | 10-13 hours |
| Toddler (1-2 years) | 11-14 hours |
| Infant (4-11 months) | 12-16 hours |
| Newborn (0-3 months) | 14-17 hours |
| Complete cycles | Time asleep | Time in bed (with 15 min to fall asleep) |
|---|---|---|
| 4 | 6 h 00 m | 6 h 15 m |
| 5 | 7 h 30 m | 7 h 45 m |
| 6 | 9 h 00 m | 9 h 15 m |
Five cycles is the usual target for an adult: 7.5 hours asleep, which lands inside the 7–9 hour guidance. A night is normally 4–6 cycles, and the cycles are not identical — deep sleep is concentrated in the first half of the night and REM sleep in the second half, which is why cutting the last hour or two costs a disproportionate share of REM.
Sleep is not one uniform state. Through the night the brain moves through non-REM stages (N1 light, N2 spindle sleep, N3 deep slow-wave) and then REM, and that full loop averages about 90 minutes — a population average, with individual cycles running anywhere from 80 to 120 minutes. An alarm that fires in the middle of deep sleep drags you up through the lighter stages, and that lag is what people call sleep inertia: the heavy, foggy feeling that can take 30 minutes or more to clear. Waking near the end of a cycle, when sleep is already light, usually feels easier.
No calculator can guarantee that, because your real cycle length is not exactly 90 minutes and varies night to night. What the grid does is put the odds in your favour. If 90 minutes never feels right after a week, try 85 or 95 — track when you naturally wake without an alarm and work backwards.
You do not fall asleep the moment you get into bed. Sleep latency for a healthy adult is typically 10–20 minutes, so every bedtime this calculator returns has 15 minutes built in. Planning to be asleep at 11:00 PM therefore means getting into bed at about 10:45 PM. Falling asleep in under five minutes is not a sign of good sleep — it usually means you are sleep-deprived.
Time in bed also is not the same as time asleep. Brief awakenings through the night (1–3 is normal, a few minutes each) mean a full night in bed usually yields 30–60 minutes less actual sleep, so if you need 7.5 hours of sleep, plan roughly 8 hours in bed.
Work backwards from your wake-up time in 90-minute blocks and add 15 minutes for falling asleep. To wake at 7:00 AM, the five-cycle bedtime is 11:15 PM, the six-cycle one is 9:45 PM. There is no single clock time that is best for everyone — what matters is duration and consistency.
Adults 18–60 need 7 or more hours; the National Sleep Foundation puts 18–64 at 7–9 hours and 65+ at 7–8. Teens need 8–10 hours and school-age children 9–12. Five 90-minute cycles is 7.5 hours.
Because you need time to fall asleep. Healthy sleep latency is 10–20 minutes, so the tool builds in 15. If you want to be asleep at 11:00 PM, get into bed at about 10:45 PM.
It tends to feel worse. Waking from deep sleep (stage N3) produces sleep inertia — grogginess that can last 30 minutes or more. Waking near a cycle boundary, when sleep is already light, usually feels easier.
Yes — change the wake-up time and the bedtimes recalculate instantly. For shift work, run it separately for each schedule and keep each one as consistent as you can.