Sleep Calculator
When to go to bed or wake up to complete whole sleep cycles.
Sleep runs in cycles of roughly ninety minutes, and waking between them feels very different from waking in the middle of one. That is why six hours of sleep can feel better than seven and a half.
Enter the time you want to wake up or go to bed, how long you take to fall asleep and how many cycles you want, and this calculator gives the matching times and the total sleep per night.
At a glance
- What you enter
- Wake up at (hour), Wake up at (minutes), Sleep cycles, Length of one cycle, Minutes to fall asleep, Sleep target per night
- What you get
- Sleep per night, Be in bed by, Be asleep by, Sleep per week, Difference from the target
- Formula shown
- Yes - every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only - always verify with a professional or official source before acting on them.
How to use the Sleep Calculator
- 1 Enter Wake up at (hour) (hours on a 24 hour clock)
- 2 Enter Wake up at (minutes)
- 3 Enter Sleep cycles - Five cycles is about seven and a half hours, six is about nine.
- 4 Enter Length of one cycle (minutes)
- 5 Enter Minutes to fall asleep (minutes)
- 6 Enter Sleep target per night (hours)
- 7 Press Calculate. You get Sleep per night, Be in bed by, Be asleep by, Sleep per week, Difference from the target, and every intermediate step stays visible under “How is this calculated?”
- 8 Change one number at a time to see what moves the result - that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
Waking at 07:00 after five cycles
The common working week pattern.
You enter
- Wake up at (hour)
- 7 hours on a 24 hour clock
- Wake up at (minutes)
- 0
- Sleep cycles
- 5
- Length of one cycle
- 90 minutes
- Minutes to fall asleep
- 15 minutes
- Sleep target per night
- 8 hours
You get
- Sleep per night
- 7.50 hours
- Be in bed by
- 23.25 hours on a 24 hour clock
- Be asleep by
- 23.50 hours on a 24 hour clock
- Sleep per week
- 52.50 hours
- Difference from the target
- 0.50 hours
Five cycles of ninety minutes is 7.5 hours of sleep, so the time to be asleep is 23:30 and the time to get into bed is 23:15. That is 52.5 hours a week and about 3.2 hours short of an eight hour target each night.
Waking at 06:30 after six cycles
A longer night on the same wake time.
You enter
- Wake up at (hour)
- 6 hours on a 24 hour clock
- Wake up at (minutes)
- 30
- Sleep cycles
- 6
- Length of one cycle
- 90 minutes
- Minutes to fall asleep
- 20 minutes
- Sleep target per night
- 8 hours
You get
- Sleep per night
- 9.00 hours
- Be in bed by
- 21.17 hours on a 24 hour clock
- Be asleep by
- 21.50 hours on a 24 hour clock
- Sleep per week
- 63.00 hours
- Difference from the target
- -1.00 hours
Six cycles is 9 hours of sleep, so the time to be asleep is 21:30 and the time to get into bed is 21:10. That meets an eight hour target with an hour to spare, at the cost of a bedtime more than two hours earlier than the five cycle example.
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Frequently asked questions
Why ninety minutes per cycle?
Ninety minutes is an average. A sleep cycle moves through light sleep, deep sleep and dreaming in roughly that order, and individual cycles range from about seventy to a hundred and twenty minutes, getting longer towards the morning.
It is a planning figure rather than a measurement. Waking at the end of a cycle generally feels better than waking in the middle of one, which is the practical point of counting them.
Does the bedtime figure include the time it takes to fall asleep?
Yes, and it is shown separately so you can see both numbers. The time to be asleep is the wake time minus the sleep itself; the time to get into bed is that minus the minutes you take to fall asleep.
Most people underestimate this by ten to twenty minutes, which is why a bedtime chosen from the sleep alone is often too late in practice.
How much sleep do adults actually need?
Seven to nine hours is the range most health bodies give for adults, and the calculator shows where a chosen number of cycles sits against a target you set. Five cycles of ninety minutes is seven and a half hours, six cycles is nine.
The figure comes from population data, not from a measurement of you. What matters more is whether you wake without an alarm and stay alert through the afternoon.
What does the share of life spent asleep mean?
It is the nightly sleep expressed as a share of a full day: eight hours a night is a third of every day, which is a third of a life spent asleep.
People are often surprised by the figure, and it is a useful way to see why sleep time is a real trade rather than an optional extra.