Sleep Calculator
Find the best bedtime or wake up time based on 90 minute sleep cycles.
Calculate your sleep times
Your sleep times
General information only, not medical advice. See a doctor if sleep problems persist.
Your sleep cycle options
Each row is a whole number of 90 minute sleep cycles. The recommended option is highlighted.
How sleep cycles work
This free sleep calculator finds the best bedtime or wake up time for anyone who wants to wake up refreshed. It runs entirely in your browser, needs no sign-up, and plans around 90 minute sleep cycles. A 2016 CDC report found that more than 1 in 3 American adults do not get enough sleep on a regular basis, so planning your sleep around full cycles is a simple step toward better rest.
How many hours of sleep do adults need each night?
The Centers for Disease Control and Prevention recommends that adults get 7 or more hours of sleep per night. Most adults feel their best with 7.5 to 9 hours, which is five or six full 90 minute sleep cycles. Sleeping less than 7 hours regularly is linked to poorer concentration, mood and long term health.
What is a sleep cycle and how long does it last?
A sleep cycle is one full pass through light sleep, deep sleep and dream sleep, known as REM sleep. Each cycle lasts about 90 minutes in most adults. A full night usually contains four to six cycles. Waking at the end of a cycle, rather than in deep sleep, usually feels easier and less groggy.
Is it better to wake up at the end of a sleep cycle?
Yes, in most cases. Waking during deep sleep often leaves you groggy and disoriented for 15 to 30 minutes, a feeling called sleep inertia. Waking at the end of a 90 minute cycle usually feels lighter because the brain is already close to wakefulness. This calculator times your bedtime so your alarm lands between cycles.
What time should I go to bed if I wake up at 7 AM?
For a 7 AM alarm, the best bedtimes are 9:46 PM for 9 hours of sleep or 11:16 PM for 7.5 hours, allowing 14 minutes to fall asleep. Both options give you whole sleep cycles and meet the 7 hour minimum for adults. If you need six hours only, 12:46 AM is the next cycle boundary.
Can I use this sleep calculator for naps?
Yes, for short naps the same cycle idea applies. A 20 to 30 minute nap refreshes you without entering deep sleep, while a full 90 minute nap completes one whole cycle. Avoid naps longer than 90 minutes late in the day, because they can make it harder to fall asleep at night.
What should I do if I often struggle to sleep?
Keep a regular sleep schedule, avoid screens and bright light before bed, and keep your bedroom dark, quiet and cool. Avoid caffeine late in the day and heavy meals close to bedtime. If sleep problems last more than a few weeks, or you often feel exhausted during the day, see a doctor for advice.
Frequently asked questions
How many sleep cycles do I need each night?
Most adults need five or six cycles, which is 7.5 to 9 hours of sleep. Four cycles, or 6 hours, can work for one night, but it is below the recommended amount for most adults if it becomes a habit.
Why does this calculator add 14 minutes to fall asleep?
Most people do not fall asleep the moment their head touches the pillow. Research on average sleep onset puts it near 10 to 20 minutes, so 14 minutes is a reasonable middle value. If you usually fall asleep faster or slower, shift the times by the difference.
What if I wake up in the middle of the night?
Waking briefly between cycles is normal. Try to stay relaxed and avoid checking the clock or your phone, since bright light and worry make it harder to drift off again. If it happens most nights, talk to a doctor.
Is 6 hours of sleep enough?
For most adults, no. Six hours is four full cycles, so you will wake at a cycle boundary, but it is below the 7 hour minimum recommended by the CDC. A small number of people function well on 6 hours, but most feel and perform better on 7.5 or more.
Does this calculator work for shift workers?
Yes. The cycle math works for any bedtime, day or night. Enter the time you need to wake up for your shift, and the calculator gives you bedtimes that land on cycle boundaries.
Should children use this sleep calculator?
This calculator is designed for adults. Children and teenagers need more sleep than adults, usually 9 to 12 hours depending on age, so the cycle options here are too short for them. Follow pediatric sleep guidance for younger ages.
Does this calculator store or send my data?
No. The calculator runs entirely in your browser. Nothing you type is uploaded, stored or shared.
More tools you may need
Planning a home upgrade too? Try our HVAC System Cost Calculator to price a new heating and cooling system. Testing your fitness? Try the Army Fitness Test Calculator, or check the Dating Standards Calculator.
