Sleep calculator
Wake up between sleep cycles, not in the middle of one.
Your files stay on your device
This tool runs entirely in your browser. What you paste is processed on your device and is never sent to a server, so it is safe to use with tokens, keys and unpublished text.
Example
Example: up at 6:15 AM for work — bedtimes for three to six sleep cycles
Someone who has to be up at 6:15 on weekdays wants to know when to go to bed. Settings: “Wake up at a set time”, Time 6:15 am, Minutes to fall asleep 15 (average), Length of a cycle 90 minutes.
- The calculator counts back whole cycles from 6:15 AM, then the 15 minutes it takes to fall asleep: 6:15 AM − 5 × 90 minutes − 15 minutes = 10:30 PM.
- Five and six cycles (7½ and 9 hours) fall inside the 7 to 9 hours adults need, so both are marked “best for adults” and shown as the best times: 9:00 PM / 10:30 PM.
- If falling asleep usually takes half an hour, set Minutes to fall asleep to 30: every bedtime moves 15 minutes earlier.
| Cycles | Sleep | Bed at (15 min to fall asleep) | Bed at (30 min) |
|---|---|---|---|
| 6 | 9 h | 9:00 PM | 8:45 PM |
| 5 | 7 h 30 min | 10:30 PM | 10:15 PM |
| 4 | 6 h | 12:00 AM | 11:45 PM |
| 3 | 4 h 30 min | 1:30 AM | 1:15 AM |
Aim for 10:30 PM, or 9:00 PM after a short night. With 100-minute cycles only 9:40 PM is marked (5 cycles, 8 h 20 min), because six would be 10 hours. With 80-minute cycles it is 10:00 PM (6 cycles, 8 h). The times are a guide, not a rule.
How it works
- Choose whether you have a time to wake up, a time to go to bed, or are going to bed now.
- Type the time (7:00, 6:30 am, 23:00) and adjust how long you usually take to fall asleep.
- Pick one of the times: five or six cycles (7½ or 9 hours) suit most adults.
Frequently asked questions
- How does the sleep calculator work?
- Sleep runs in cycles of about 90 minutes, from light sleep to deep sleep and REM. Waking at the end of a cycle, rather than in deep sleep, tends to feel easier. The calculator counts back (or forward) whole cycles from your time, plus the minutes you take to fall asleep.
- How many hours of sleep do I need?
- Adults need 7 to 9 hours, teenagers 8 to 10 and school-age children 9 to 12, according to the American Academy of Sleep Medicine. Five or six cycles fit the adult range.
- Is a cycle always 90 minutes?
- No — cycles last 70 to 120 minutes and vary from night to night. If you often wake just before the alarm, try 80 or 100 minutes.
- What if I wake up tired anyway?
- Regular hours matter more than cycle timing. Persistent tiredness, snoring or pauses in breathing are worth raising with a doctor.
- What time should I go to bed if I wake up at 6 AM?
- At 10:15 PM for five cycles (7½ hours) or 8:45 PM for six (9 hours), counting 15 minutes to fall asleep. Four cycles would mean 11:45 PM, only 6 hours, which is below what adults need.
- If I go to bed at 11 PM, when should I wake up?
- At 6:45 AM after five cycles or 8:15 AM after six, counting 15 minutes to fall asleep. Choose “Go to bed at a set time” and type 11 pm. 5:15 AM (four cycles) is listed too, but it is only 6 hours.
- Is anything uploaded?
- No. It is worked out in your browser, and nothing you type leaves your computer.