Sleep Calculator
This sleep calculator works out what time to go to bed so you wake up at the end of a sleep cycle, or what time to wake up if you go to bed at a set time or right now. It counts in sleep cycles of about 90 minutes and adds the 15 minutes or so most people need to fall asleep. Choose Wake up at, Go to bed at or Go to bed now, enter a time if needed, and select Calculate. The results are estimates, not medical advice.
We use the current time on your device, so it matches the country and time zone you are in.
Fill in both boxes, or untick this option to use the usual 15 minutes and 3 to 6 cycles.
Please enter a time.
How to Use the Sleep Calculator
- Choose one of three options: Wake up at (the calculator gives you bedtimes), Go to bed at (it gives you wake-up times), or Go to bed now.
- Enter the time. You can skip this step for “go to bed now”, which uses your device’s clock, so it follows your own country and time zone.
- Choose the age group, then select Calculate. Highlighted times give an amount of sleep in the recommended range for that age group. If you want to use your own numbers, tick “I want to enter my own fall-asleep time and sleep cycles” and fill in both boxes that appear: the minutes you take to fall asleep and the number of 90-minute cycles. If either box is empty the calculator asks you to fill it in or untick the option.
Sleep Calculator — How It Works
Wake-up time = bedtime + 15 minutes to fall asleep + (cycles × 90 minutes)
A sleep cycle is the pattern your brain repeats through the night: light sleep, deeper sleep, then REM sleep, where most dreaming happens. On average a cycle lasts about 90 minutes, and a typical night has four to six of them. The calculator counts in whole cycles so your alarm lands at the end of one, when sleep is lighter, rather than part-way through deep sleep, which is when waking tends to feel groggiest.
It also adds the time you need to fall asleep. For healthy adults that is usually 10 to 20 minutes, so the calculator uses 15. If you usually take longer or shorter, tick the option under the age group and enter your own minutes. Because the first cycle of the night is often shorter and later ones longer, the 90-minute cycle is an average, not a measurement of your own sleep.
Sleep Calculator Example
Say you need to be up at 6:30 am. The calculator allows 15 minutes to fall asleep and counts in 90-minute cycles. Six cycles is 9 hours of sleep, so you would go to bed at 9:15 pm. Five cycles is 7 hours 30 minutes, which means a bedtime of 10:45 pm. Four cycles is only 6 hours and would mean going to bed at 12:15 am. For an adult, five or six cycles is the aim, so 10:45 pm or 9:15 pm are the times worth choosing.
What Time Should I Go to Bed if I Wake Up at 6am, 7am or 8am?
This table shows the bedtime for common wake-up times counting 90-minute cycles and 15 minutes to fall asleep. Use the 5-cycle column for 7 hours 30 minutes of sleep, or the 6-cycle column for 9 hours. The 4-cycle column is shown for nights when you have less time, but 6 hours is below the amount recommended for adults.
| Wake up at | 6 cycles (9 h) | 5 cycles (7 h 30 min) | 4 cycles (6 h) |
|---|---|---|---|
| 5:00 am | 7:45 pm | 9:15 pm | 10:45 pm |
| 5:30 am | 8:15 pm | 9:45 pm | 11:15 pm |
| 6:00 am | 8:45 pm | 10:15 pm | 11:45 pm |
| 6:30 am | 9:15 pm | 10:45 pm | 12:15 am |
| 7:00 am | 9:45 pm | 11:15 pm | 12:45 am |
| 7:30 am | 10:15 pm | 11:45 pm | 1:15 am |
| 8:00 am | 10:45 pm | 12:15 am | 1:45 am |
| 9:00 am | 11:45 pm | 1:15 am | 2:45 am |
Bedtime is the time you get into bed and try to sleep. Each time includes 15 minutes to fall asleep and uses 90-minute cycles.
What Time Should I Wake Up if I Go to Bed at 10pm or 11pm?
If you already know when you are going to bed, this table shows when each number of full cycles ends. Waking after five or six cycles gives 7 hours 30 minutes or 9 hours of sleep.
| Go to bed at | 4 cycles (6 h) | 5 cycles (7 h 30 min) | 6 cycles (9 h) |
|---|---|---|---|
| 9:00 pm | 3:15 am | 4:45 am | 6:15 am |
| 9:30 pm | 3:45 am | 5:15 am | 6:45 am |
| 10:00 pm | 4:15 am | 5:45 am | 7:15 am |
| 10:30 pm | 4:45 am | 6:15 am | 7:45 am |
| 11:00 pm | 5:15 am | 6:45 am | 8:15 am |
| 11:30 pm | 5:45 am | 7:15 am | 8:45 am |
| midnight | 6:15 am | 7:45 am | 9:15 am |
Wake-up times are the next morning and include 15 minutes to fall asleep, using 90-minute cycles.
Sleep Cycles and Hours of Sleep
Each full 90-minute cycle adds an hour and a half of sleep. The table converts cycles to hours, with and without the 15 minutes it takes to fall asleep. Most adults are recommended 7 or more hours, which is five cycles or more. Read how many sleep cycles you need per night for the full explanation.
| Sleep cycles | Time asleep | Time in bed (with 15 min to fall asleep) |
|---|---|---|
| 1 | 1 h 30 min | 1 h 45 min |
| 2 | 3 h | 3 h 15 min |
| 3 | 4 h 30 min | 4 h 45 min |
| 4 | 6 h | 6 h 15 min |
| 5 | 7 h 30 min | 7 h 45 min |
| 6 | 9 h | 9 h 15 min |
Key Features & Benefits of This Sleep Calculator
- Bedtime and wake-up time in one tool — count back from the time you must get up, forward from a bedtime, or forward from right now.
- Time to fall asleep included — every time already allows about 15 minutes to drop off, so you can use it as it is, or enter your own minutes.
- Recommended times highlighted — pick an age group and the times that give a suitable amount of sleep stand out.
- Uses your own time zone and time format — “Go to bed now” follows the clock in the country you are in, and results use the 12-hour or 24-hour format your device uses.
- Instant, free and private — runs entirely in your browser, no sign-up, nothing stored.
Good to know
This calculator gives estimates and is not medical advice. Sleep cycles vary from person to person and from night to night, and only a sleep study can measure your sleep stages, so aim for the right amount of sleep and regular bed and wake-up times rather than an exact minute. The 90-minute cycle is an adult average. If you regularly take much longer than 20 to 30 minutes to fall asleep, feel exhausted despite enough hours in bed, or snore loudly or stop breathing in your sleep, speak with a doctor.
Sleep Calculator — FAQs
What time should I go to bed if I wake up at 6am?
Counting 90-minute cycles and 15 minutes to fall asleep, 10:15 pm gives five full sleep cycles (7 hours 30 minutes of sleep) and 8:45 pm gives six (9 hours). 11:45 pm gives four cycles, which is 6 hours and below the 7 or more hours recommended for adults. These times include 15 minutes to fall asleep.
What time should I wake up if I go to sleep now?
Choose “Go to bed now” and select Calculate. The calculator reads the current time on your device (so it uses your own time zone), adds 15 minutes to fall asleep, then lists wake-up times after three to six sleep cycles (4 hours 30 minutes to 9 hours of sleep), earliest first. For example, if you go to bed at 11:00 pm, five cycles ends at 6:45 am and six cycles at 8:15 am.
What time should I wake up if I go to sleep at 10pm?
If you go to bed at 10:00 pm and take 15 minutes to fall asleep, four cycles end at 4:15 am, five cycles at 5:45 am and six cycles at 7:15 am. Five or six cycles fit the 7 to 9 hours most adults need.
How long is a sleep cycle?
About 90 minutes on average. The first cycle of the night is often shorter, around 70 to 100 minutes, and later cycles tend to last 90 to 120 minutes, so 90 minutes is an average rather than an exact figure for you.
How many sleep cycles do I need?
A typical night includes four to six cycles. For an adult, five cycles (7 hours 30 minutes) or six cycles (9 hours) fit the recommended 7 or more hours, while four cycles (6 hours) fall short. Our guide explains how many sleep cycles you need per night.
How long does it take to fall asleep?
A normal time to fall asleep is about 10 to 20 minutes for healthy adults, which is why the calculator uses 15 minutes. If you usually fall asleep faster or slower, tick the option under the age group in the calculator and enter your own minutes. If it regularly takes much longer than 20 to 30 minutes, it can be a sign of insomnia or another sleep problem, so talk to a doctor.
Does waking up at the end of a sleep cycle stop grogginess?
It can help, but it is not guaranteed. Grogginess after waking, called sleep inertia, is most likely when you wake abruptly from deep sleep and usually lasts 15 to 60 minutes. Because cycle length varies from night to night, a calculator can only estimate where a cycle ends. Enough total sleep and regular bed and wake-up times also help, so treat the results as a guide rather than a precise alarm.
How many hours of sleep do adults need?
The CDC recommends 7 or more hours for adults aged 18 to 60, 7 to 9 hours for ages 61 to 64 and 7 to 8 hours for ages 65 and over. Teenagers aged 13 to 17 are recommended 8 to 10 hours.
Sources and review
Sources last checked: . These sources give the background for this calculator. They are general information and do not replace advice from your doctor.
- CDC: About Sleep: recommended hours of sleep by age, including 7 or more hours for adults and 8 to 10 hours for teenagers aged 13 to 17.
- Sleep Foundation: How Much Sleep Do Adults Need?: most healthy adults need between 7 and 9 hours of sleep each night.
- Sleep Foundation: Stages of Sleep: a sleep cycle lasts about 90 minutes on average, and a typical night has four to six cycles.
- Sleep Foundation: Sleep Latency: a normal time to fall asleep is about 10 to 20 minutes.
- Cleveland Clinic: Sleep Inertia: grogginess after waking usually lasts 15 to 60 minutes and is most likely after waking abruptly from deep sleep.
- NHS Every Mind Matters: Fall asleep faster and sleep better: going to bed and getting up at similar times each day, and a quiet, dark, cool bedroom.