Daily life & Islamic
Sleep Calculator
Waking in the middle of deep sleep leaves you groggy. This calculator works in 90-minute sleep cycles: tell it when you need to wake up to get the best bedtimes, or when you are going to bed to get the best wake-up times.
How to use the Sleep Calculator
- Choose wake-up or bedtime mode.
- Enter the time.
- Set how long you usually take to fall asleep.
- Pick a time from the list.
Formula
Example
To wake at 6:30 AM after 5 cycles (7.5 hours) with 15 minutes to fall asleep, go to bed at 10:45 PM.
Better sleep
- Keep the same wake time every day
- Avoid screens 30-60 minutes before bed
- Keep the bedroom cool and dark
- Limit caffeine after midday
Why 90-minute cycles matter
During the night your sleep moves through light sleep, deep sleep and dream (REM) sleep in cycles of roughly 90 minutes. Waking up at the end of a cycle usually feels easier than being woken from deep sleep, even if the total time is a little shorter.
Sleep and daily routine
- Fajr and early starts: work backwards from your wake-up time
- Night shifts and freelancers working US hours: keep the same sleep window every day, even on weekends
- Students before exams: a full night’s sleep helps memory more than late-night study
- A short nap of 20 minutes refreshes without grogginess
When to see a doctor
If you often feel tired despite enough hours in bed, snore loudly, or wake up gasping, talk to a doctor - these can be signs of a sleep disorder.
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Frequently asked questions
How much sleep do adults need?
7-9 hours for most adults.
Teens?
8-10 hours.
Are cycles always 90 minutes?
They range from about 80 to 120 minutes.
Can I catch up on weekends?
Partly, but a steady schedule works better.
Does this work for naps?
For naps, either keep them to about 20 minutes or take a full 90-minute cycle.
What if I take longer to fall asleep?
Change the minutes-to-fall-asleep box and the times update.
This tool gives general information, not medical advice. Talk to your doctor or another qualified health professional about your own situation. Your inputs stay in your browser.
Last updated: November 2026