Sleep Calculator
Find optimal bedtimes and wake times based on 90-minute sleep cycles.
9:45 PM
6 cycles · 9h
11:15 PM
5 cycles · 7.5h
12:45 AM
4 cycles · 6h
2:15 AM
3 cycles · 4.5h
Each sleep cycle lasts ~90 minutes. The calculator adds 15 minutes for falling asleep. Aim for 5–6 complete cycles for optimal rest.
What is a Sleep Calculator?
A sleep calculator helps you time your sleep to complete full 90-minute sleep cycles. Each cycle takes you through light sleep, deep sleep, and REM sleep. Waking up between cycles — rather than in the middle of one — helps you feel more refreshed and alert, even with the same total hours of sleep. This tool accounts for the average 15 minutes it takes to fall asleep and calculates optimal times for 3 to 6 complete cycles.
How to Use
- Choose your mode: set a wake-up time and find the best bedtimes, set a bedtime and find the best wake times, or go to bed now and see when to set your alarm.
- Enter the relevant time if applicable.
- Review the suggested times — aim for 5–6 cycles (7.5–9 hours) for optimal rest.
Frequently Asked Questions
Why 90-minute cycles?
A complete sleep cycle lasts approximately 90 minutes and includes all stages of sleep: light sleep (N1 and N2), deep sleep (N3), and REM sleep. The 90-minute figure is an average — individual cycles range from 70 to 120 minutes. Waking at the end of a cycle, during light sleep, leaves you feeling naturally alert rather than groggy.
How many cycles do I need?
Most adults need 5–6 complete cycles (7.5–9 hours) per night for optimal health and cognitive function. Four cycles (6 hours) is the minimum for adequate functioning, though chronic 6-hour sleep has been shown to impair performance comparably to moderate sleep deprivation. Teenagers typically need 8–10 hours, while older adults may function well on 7–8 hours.
Does it really take 15 minutes to fall asleep?
The average sleep onset latency — the time it takes to fall asleep — is about 10–20 minutes for healthy adults. This calculator uses 15 minutes as a middle estimate. If you consistently fall asleep in under 5 minutes, it may indicate sleep deprivation. If it regularly takes more than 30 minutes, you may have insomnia and should consider speaking with a healthcare provider.
