Find the best times to sleep or wake based on 90-minute sleep cycles.
Calculated instantly in your browser.
How do you calculate the best time to sleep or wake up?
Each sleep cycle is about 90 minutes, and people take roughly 14 minutes to fall asleep, so the tool counts back or forward in whole cycles from your chosen time. Most adults do best on 5–6 cycles (7.5–9 hours). To wake at 7:00 AM, good bedtimes are about 9:46 PM (6 cycles) or 11:16 PM (5 cycles).
Understanding your result
Most adults do best on 5–6 cycles (7.5–9 hours). Waking between cycles avoids the grogginess of waking mid-cycle.
Formula and method
Each cycle is about 90 minutes, and people take roughly 14 minutes to fall asleep. The tool counts back or forward in whole cycles from your chosen time.
Assumptions and limitations
This is a general timing guide based on average 90-minute cycles, not medical advice, and sleep varies by individual. Real cycle length, how quickly you fall asleep and how much sleep you need differ from person to person and night to night. For persistent sleep problems, speak to a qualified professional.
Worked example
To wake at 7:00 AM, good bedtimes are about 9:46 PM (6 cycles) or 11:16 PM (5 cycles).
How to use this tool
- Choose whether you’re setting a wake time or a sleep time.
- Enter the time.
- Press Calculate to see the recommended times.
About the Sleep Calculator
The Sleep Calculator suggests bedtimes or wake-up times that fall between 90-minute sleep cycles, so you wake at the lightest part of sleep and feel more rested.
Who should use this tool
Anyone wanting to plan a bedtime or wake-up time around 90-minute sleep cycles to reduce grogginess. Useful for setting an alarm that lands between cycles, planning an early start, or working back from a fixed wake time to a range of suitable bedtimes.
Benefits
- Suggests bed or wake times aligned to sleep cycles
- Aims to wake you at a lighter sleep stage
- Accounts for the time taken to fall asleep
- Calculates privately in your browser, no account
Practical use cases
- Choosing a bedtime for a fixed wake-up alarm
- Planning an early start without waking mid-cycle
- Finding wake times if you go to bed now
- Setting a consistent sleep schedule around cycles
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Frequently asked questions
Why 90 minutes?
A full sleep cycle through light, deep and REM sleep averages about 90 minutes, though it varies between people.
Why does the tool add time before I fall asleep?
People rarely sleep the instant they lie down, so the tool allows roughly fourteen minutes to drift off before counting cycles. Including this makes the suggested times more realistic, since the aim is to complete whole 90-minute cycles from when you actually fall asleep, not from when you get into bed.
How many sleep cycles should I aim for?
Most adults do well on five to six cycles a night, which is about seven and a half to nine hours. The tool offers times for several cycle counts so you can pick one that fits your schedule. Individual needs vary, so use it as a flexible guide rather than a fixed rule.