About the Sleep Calculator
During the night you move through light sleep (stages N1โN2), deep sleep (N3) and REM sleep. One round of these stages is a sleep cycle, and it lasts about 90 minutes on average. If your alarm goes off during deep sleep you feel groggy, but waking at the end of a cycle, when sleep is light, feels much easier.
This calculator adds the time it takes you to fall asleep (15 minutes by default) and suggests times that fit 6, 5 or 4 full cycles (9 h, 7 h 30 min or 6 h of sleep).
How to use
- Choose a mode: start from the time you need to wake up, or from the time you go to bed.
- Enter your wake-up time (or bedtime).
- Enter how long you usually take to fall asleep โ typically 10โ20 minutes.
- Going to sleep right now? Tap If I go to sleep now. The times marked Best give you 5โ6 cycles.
Example: waking up at 7:00 AM
| Go to bed at | Sleep | Cycles |
|---|---|---|
| 9:45 PM | 9 h | 6 |
| 11:15 PM | 7 h 30 min | 5 |
| 12:45 AM | 6 h | 4 |
These times assume 15 minutes to fall asleep. Formula: bedtime = wake-up time โ time to fall asleep โ 90 minutes ร number of cycles.
How much sleep do you need?
| Age | Recommended sleep |
|---|---|
| School age (6โ13) | 9โ11 hours |
| Teenagers (14โ17) | 8โ10 hours |
| Adults (18โ64) | 7โ9 hours |
| Older adults (65+) | 7โ8 hours |
Recommendations from the National Sleep Foundation. Getting enough sleep matters more than hitting cycles exactly, and keeping the same bedtime and wake-up time every day helps most.
FAQ
Is a sleep cycle really 90 minutes?
90 minutes is just the average. Cycles vary between people and across the night, from about 70 to 120 minutes. Try the suggested times for a few days and adjust to whatever leaves you feeling most refreshed.
Is 4 cycles (6 hours) enough?
Now and then itโs fine, but adults who regularly sleep 6 hours or less have poorer concentration and higher health risks. Aim for at least 5 cycles (7 h 30 min) when you can.
How long should a nap be?
A short nap of 20 minutes or less, before you reach deep sleep, or a full 90-minute cycle tends to feel refreshing. Naps of 30โ60 minutes often end in deep sleep and can leave you groggy.