Bedtime Calculator: When to Go to Sleep for Your Alarm
Bedtimes that fit whole 90-minute sleep cycles before your alarm, plus 15 minutes to fall asleep.
Inputs
- Wake time
- 06:30
- Sleep duration
- 7h 30m
- Other options
- 00:15 (4 cycles); 21:15 (6 cycles)
- Count back 90-minute cycles from wake time, minus ~15 min to fall asleep.
Use this calculator on your own site
Free embed
- Two lines of HTML, unlimited views
- Shows a small CalculateEveryday bar, with a credit link under the calculator
What each Bedtime input means
- Wake-up time
- When your alarm goes off. Any time works; shift workers can enter an afternoon wake-up.
- Sleep cycles
- How many 90-minute cycles to fit in, from 3 to 6. Five is 7.5 hours of sleep, above the CDC's 7-hour minimum for adults; four is only 6 hours.
Bedtime formula
bedtime = wake time − cycles × 90 min − 15 min to fall asleep
Sleep runs in cycles of light, deep and REM sleep that repeat through the night — every 80 to 100 minutes, according to the National Heart, Lung, and Blood Institute, usually four to six times. Waking at the end of a cycle, rather than in the middle of deep sleep, is the idea behind this kind of planner. Working back from the alarm, the page subtracts whole cycles of the conventional 90 minutes and then 15 minutes to fall asleep, and lists bedtimes for several cycle counts. The CDC recommends at least 7 hours a night for adults, which is five cycles.
Bedtime worked example
To wake at 06:30 after five cycles: 5 × 90 = 450 minutes (7.5 hours) of sleep, plus 15 minutes to drop off, is 7 hours 45 minutes before the alarm — in bed by 22:45. Six cycles means 21:15; four means 00:15, but that is only 6 hours of sleep, under the CDC's 7.
More Bedtime examples
Waking at 07:00 after six cycles — 9 hours of sleep — means being in bed at 21:45. Five cycles moves it to 23:15, and four to 00:45.
An early-shift alarm at 04:45: five cycles plus 15 minutes to fall asleep puts the bedtime at 21:00.
A night-shift worker who must be up at 14:00: five cycles and 15 minutes to fall asleep put the bedtime at 06:15, straight after the shift.
Where the Bedtime calculator can give the wrong answer
- Cycle length varies from person to person and through the night, so these times are a guide, not a promise of waking refreshed.
- If you usually take longer than 15 minutes to fall asleep, move the bedtime earlier by the difference.
- Shift workers sleeping by day can use it the same way: enter the time you must get up.
- The health sleep-cycle calculator works the other way, from bedtime to wake times.
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Bedtime reference table
| Alarm | 4 cycles (6 h) | 5 cycles (7.5 h) | 6 cycles (9 h) |
|---|---|---|---|
| 05:00 | 22:45 | 21:15 | 19:45 |
| 05:30 | 23:15 | 21:45 | 20:15 |
| 06:00 | 23:45 | 22:15 | 20:45 |
| 06:30 | 00:15 | 22:45 | 21:15 |
| 07:00 | 00:45 | 23:15 | 21:45 |
| 07:30 | 01:15 | 23:45 | 22:15 |
| 08:00 | 01:45 | 00:15 | 22:45 |
Bedtime FAQ
- For five 90-minute cycles plus 15 minutes to fall asleep, at 22:15 (10:15 pm). For six cycles, 20:45.
- About 80 to 100 minutes, according to the NHLBI, repeating four to six times a night. Planners like this one use 90.
- At least 7 hours a night, according to the CDC — five 90-minute cycles is 7.5 hours.
- Most people take a little while to fall asleep. The 15 minutes is a planning allowance; change the bedtime if you know you take longer.
- Not for most adults by the CDC's guidance of 7 or more hours a night. Four 90-minute cycles is 6 hours, which is why the page counts five as the normal choice.
- For five cycles, 23:15 (11:15 pm); for six, 21:45. Four cycles means 00:45, but that is only 6 hours of sleep.
- More than adults. The CDC's guidance is 9 to 12 hours a night for children aged 6 to 12 and 8 to 10 hours for teenagers aged 13 to 18 — six 90-minute cycles is 9 hours.
- The one that leaves you at least 7 hours before you have to get up. The cycle arithmetic only fine-tunes it, by placing the alarm at the end of a cycle rather than in the middle of one.
- Not a short one: the smallest plan here is three 90-minute cycles, 4.5 hours. A nap is usually much shorter than a full cycle.
- No. It assumes unbroken cycles; if you usually wake for a while, go to bed that much earlier.