Sleep Calculator: When to Wake Up or Go to Bed
Bedtimes and wake-up times that line up with 90-minute sleep cycles.
Use via API
Bedtimes for a wake-up time, or wake-up times for a bedtime, timed to whole 90-minute sleep cycles (6, 5, 4 or 3 cycles). Send JSON, get JSON back.
POST https://pithlab.com/api/v1/tools/sleep-calculator
curl https://pithlab.com/api/v1/tools/sleep-calculator \
-H "Authorization: Bearer $PITHLAB_KEY" \
-H "Content-Type: application/json" \
-d '{"mode":"wake","time":"07:00"}'About the Sleep Calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles plus the time it takes you to fall asleep, so you wake between cycles.
How to use the Sleep Calculator
- Choose whether you know when you need to wake up, or when you're going to bed.
- Enter the time, or press “Go to bed now” to use the current time. Adjust how long you usually take to fall asleep (15 minutes by default).
- Pick one of the suggested times. Five or six cycles (7.5 to 9 hours of sleep) is the usual target for adults.
Examples
Input
Wake at 07:00, 15 min to fall asleep
Output
To wake at 7:00 AM, go to bed at 9:45 PM (6 cycles), 11:15 PM (5), 12:45 AM (4) or 2:15 AM (3)
Input
Bed at 23:00, 15 min to fall asleep
Output
In bed at 11:00 PM, wake at 8:15 AM (6 cycles), 6:45 AM (5), 5:15 AM (4) or 3:45 AM (3)
Input
Wake at 05:30, 5 min to fall asleep
Output
To wake at 5:30 AM, go to bed at 8:25 PM (6 cycles), 9:55 PM (5), 11:25 PM (4) or 12:55 AM (3)
Frequently asked questions
Why 90-minute cycles?
Sleep moves through light, deep and REM stages in cycles that average roughly 90 minutes in adults. Waking at the end of a cycle, in lighter sleep, tends to feel less groggy than being woken from deep sleep. 90 minutes is only an average: real cycles range from about 70 to 120 minutes and change through the night, so treat the times as a guide rather than an exact schedule.
How much sleep do adults need?
Most health bodies recommend 7 or more hours for adults, which is why 5 cycles (7.5 hours) and 6 cycles (9 hours) are highlighted. Teenagers and children need more. Three or four cycles are shown for short nights, not as a habit.
What does “time to fall asleep” do?
It's added before the first cycle starts. Most people take 10 to 20 minutes to fall asleep; if you're usually out in 5 minutes, or lie awake for half an hour, change it so the times fit you.
Is this medical advice?
No. It's simple arithmetic on average cycle lengths. If you regularly struggle to sleep or feel tired after a full night, talk to a doctor.