Health & Body Tables
Sleep Cycle Table: Bedtime and Wake Times
Sleep runs in cycles of roughly 90 minutes, moving from light sleep through deep sleep and into REM before starting again. Waking at the end of a cycle, in the light phase, produces a different morning from waking in the middle of deep sleep — which is why six hours can feel better than seven and a half. The tables below work in whole cycles rather than whole hours for that reason.
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Two numbers do the arithmetic. The cycle length is 90 minutes, a population average: normal cycles run from about 70 to 110 minutes, and the first cycle of the night is usually shorter than the later ones. The second number is the time it takes to fall asleep, about 14 minutes for a healthy adult. Together they mean a 23:00 bedtime with six cycles ends at 08:14, not 08:00.
This is a planning tool, not a diagnosis. If you need an alarm to wake up, feel unrefreshed after eight hours, snore heavily or fall asleep during the day, the problem is not the schedule — it is worth talking to a clinician, because sleep apnoea and other disorders do not respond to bedtime arithmetic.
If you go to bed at this time, the alarm rings at
| Bedtime | 4 cycles (6 h) | 5 cycles (7.5 h) | 6 cycles (9 h) |
|---|---|---|---|
| 21:00 | 03:14 | 04:44 | 06:14 |
| 21:30 | 03:44 | 05:14 | 06:44 |
| 22:00 | 04:14 | 05:44 | 07:14 |
| 22:30 | 04:44 | 06:14 | 07:44 |
| 23:00 | 05:14 | 06:44 | 08:14 |
| 23:30 | 05:44 | 07:14 | 08:44 |
| 00:00 | 06:14 | 07:44 | 09:14 |
| 00:30 | 06:44 | 08:14 | 09:44 |
| 01:00 | 07:14 | 08:44 | 10:14 |
Waking between cycles, at the end of REM, is what makes a six-hour night feel better than a seven-hour one interrupted mid-cycle. The 14 minutes is the average time to fall asleep, not a fixed cost.
If you must be up at this time, go to bed at
| Wake time | 6 cycles (9 h) | 5 cycles (7.5 h) | 4 cycles (6 h) |
|---|---|---|---|
| 05:00 | 19:46 | 21:16 | 22:46 |
| 05:30 | 20:16 | 21:46 | 23:16 |
| 06:00 | 20:46 | 22:16 | 23:46 |
| 06:30 | 21:16 | 22:46 | 00:16 |
| 07:00 | 21:46 | 23:16 | 00:46 |
| 07:30 | 22:16 | 23:46 | 01:16 |
| 08:00 | 22:46 | 00:16 | 01:46 |
| 08:30 | 23:16 | 00:46 | 02:16 |
| 09:00 | 23:46 | 01:16 | 02:46 |
Work backwards from the alarm, not forwards from bedtime. Most people cannot choose when they wake, so the second table is the one that actually gets used on a work night.
Recommended sleep by age, and what that means in 90 minute cycles
| Age group | Recommended hours | Cycles at the low end | Cycles at the high end |
|---|---|---|---|
| 0-3 months | 14-17 h | 9.3 | 11.3 |
| 4-11 months | 12-15 h | 8 | 10 |
| 1-2 years | 11-14 h | 7.3 | 9.3 |
| 3-5 years | 10-13 h | 6.7 | 8.7 |
| 6-13 years | 9-11 h | 6 | 7.3 |
| 14-17 years | 8-10 h | 5.3 | 6.7 |
| 18-25 years | 7-9 h | 4.7 | 6 |
| 26-64 years | 7-9 h | 4.7 | 6 |
| 65 and over | 7-8 h | 4.7 | 5.3 |
Recommendations from the American Academy of Sleep Medicine consensus statement, endorsed by the Sleep Research Society. The cycle count is arithmetic — the recommendation is in hours, not cycles.
How to Use These Tables
- Choose the number of cycles first. Five cycles is 7.5 hours, the usual adult target; six is 9 hours and suits teenagers and anyone catching up after a short night.
- Add 14 minutes to your bedtime before counting cycles. Going to bed at 22:30 means sleep starts at 22:44, so five cycles end at 06:14.
- Set the alarm for the end of a cycle rather than a round number. 06:15 is a worse alarm than 06:14 for a 22:30 bedtime, and 07:00 is mid-cycle.
- On a short night, cut a whole cycle rather than an hour. Four cycles plus the drop-off allowance is a coherent 6 hours 14 minutes; six hours flat lands in the middle of the fifth cycle.
- Use the age table as a range, not a target. A 40-year-old needs seven to nine hours, which is four to six cycles, and either end of that range is normal.
Common Questions
Is a sleep cycle really 90 minutes?
On average, yes, but the range across healthy adults is roughly 70 to 110 minutes and it varies within a single night. The 90 minute figure is a planning convention, not a measurement of you.
Why add 14 minutes to the bedtime?
Because lying down is not the same as sleeping. Sleep onset latency averages about 14 minutes for adults; if yours is consistently over 30 minutes, that is itself worth mentioning to a doctor.
Is 6 hours of sleep enough?
For most adults, no. The consensus recommendation is seven to nine hours, and consistently sleeping six is associated with impaired glucose control and reduced performance even when the person feels adapted to it.
Does waking mid-cycle really matter?
It affects how groggy you feel on waking, because deep sleep produces sleep inertia. It does not change how much sleep you got — a seven-hour night cut mid-cycle is still seven hours, it just feels worse for the first twenty minutes.
Should I use this if I work shifts?
The cycle arithmetic still applies, but the circadian clock does not follow the shift. Sleeping 09:00 to 16:00 gives you the cycles without the darkness that deep sleep depends on, which is why shift workers often need more time in bed for the same recovery.
How accurate is the age table?
It is a consensus range from the American Academy of Sleep Medicine, based on population evidence. Individual need varies, and quality matters as much as duration — eight fragmented hours are not equivalent to eight continuous ones.
More Health & Body Tables
Sources
- Recommended amount of sleep for a healthy adult — joint consensus statement — American Academy of Sleep Medicine and Sleep Research Society
- Sleep and sleep disorders — data and statistics — Centers for Disease Control and Prevention
- Your guide to healthy sleep — National Heart, Lung, and Blood Institute
Filed with Health calculations.