Tool
Sleep Calculator: Bedtime, Wake-Up and Nap Times
This sleep calculator counts back from the time you need to be up, in whole sleep cycles, and shows when to be in bed. It also works the other way, from a bedtime to wake-up times, and has a nap mode. Each result is checked against the CDC's recommended hours for your age.
Estimate
To wake up at 7:00 AM, be in bed by:
| In bed by | Sleep | Cycles | Ages 18–60: 7 or more hours |
|---|---|---|---|
| 9:45 PM | 9 hours | 6 | In the range |
| 11:15 PM | 7.5 hours | 5 | In the range |
| 12:45 AM | 6 hours | 4 | Below the range |
Times include 15 minutes to fall asleep.
How it works
A night is counted in whole sleep cycles. Bedtime = wake-up time − cycles × 90 minutes − minutes to fall asleep; wake-up time = bedtime + minutes to fall asleep + cycles × 90 minutes. Each row is checked against the CDC’s recommended hours for the age you pick. Naps follow NIOSH’s advice: a short nap with an alarm 15–30 minutes after lying down, or one full cycle.
- Length of one sleep cycle (middle of NHLBI's 80–100 minute range)
- 90 min [1]
- A sleep cycle starts over every
- 80–100 min [1]
- Usual number of cycles per night
- 4–6 [1]
- Time to fall asleep (default; NIOSH suggests relaxation help if it takes longer than 15–25 minutes)
- 15 min [2]
- Normal sleep onset takes up to about
- 25 min [3]
- Short nap — set an alarm for
- 15–30 min [4]
- Full-cycle nap — predicted end of a sleep cycle
- 90 min [4]
- Recommended sleep, ages 6–12
- 9–12 hours [5]
- Recommended sleep, ages 13–17
- 8–10 hours [5]
- Recommended sleep, ages 18–60 (7 or more)
- 7 hours [5]
- Recommended sleep, ages 61–64
- 7–9 hours [5]
- Recommended sleep, ages 65 and older
- 7–8 hours [5]
How the sleep calculator works
Sleep runs in cycles. According to the NHLBI, part of the National Institutes of Health, a sleep cycle starts over every 80 to 100 minutes, and most nights have four to six of them. The calculator uses 90 minutes per cycle, the middle of that range, and adds the time you need to fall asleep.
- Bedtime = wake-up time − cycles × 90 minutes − minutes to fall asleep.
- Wake-up time = bedtime + minutes to fall asleep + cycles × 90 minutes.
The minutes to fall asleep start at 15, and you can change them. CDC guidance for nurses suggests relaxation techniques when falling asleep takes longer than 15 to 25 minutes, and another NIOSH training page calls up to about 25 minutes normal. If you know you're a slow starter, put in your own number.
Every default is listed under the result, with a link to its source.
How to read your result
Each row is one option: a time, the hours of sleep it gives you and the number of cycles. The last column checks those hours against the CDC's recommended range for the age you picked. Rows in the range are highlighted.
Pick the latest bedtime in the range that you'll actually keep. A 9:45 p.m. bedtime you skip three nights a week does less than an 11:15 p.m. one you keep every night.
Night-shift note: my alarm has gone off at 4:10 a.m. on weekdays since 2016, and I count back from it to set my bedtime. Five cycles and 15 minutes puts me in bed by 8:25 p.m. Margo calls this "a cry for help". She goes to bed at 9:30, which I call "a lifestyle choice from 1955". Biscuit sleeps whenever he likes.
Cycle lengths differ from person to person and from one part of the night to the next, so the times are estimates. Treat them as a plan, not an appointment. If you wake up a little before the alarm, that's the calculator being close, not wrong.
Naps
Nap mode follows NIOSH's advice. For a short nap, set an alarm 15 to 30 minutes after you lie down. For a longer one, plan a full cycle: the minutes to fall asleep plus about 90 minutes. Waking up after about an hour, in deep sleep, tends to be the groggiest choice. A short nap is the one NIOSH recommends for people on a daytime schedule, because it doesn't get in the way of sleep that night.
What the calculator can't do
It can tell you when to set an alarm. It can't tell you why you're tired, and it can't make you fall asleep on schedule. It stores nothing and asks for nothing beyond the times you type in.
Sleep well.
Related
Questions people ask
How many hours of sleep do I need?
It depends on your age. The CDC's table says adults 18 to 60 need 7 or more hours, adults 61 to 64 need 7 to 9 hours and adults 65 and older need 7 to 8 hours. Teens 13 to 17 need 8 to 10 hours, and kids 6 to 12 need 9 to 12 hours. Pick your age in the calculator and the rows that fit are marked.
Is 6 hours of sleep enough?
For most adults the CDC's answer is no: the recommendation for ages 18 to 60 is 7 or more hours. That's why a 4-cycle night, 6 hours, shows up in the calculator as below the range for adults. If you often wake up after 6 hours and can't get back to sleep, that's worth mentioning to your doctor.
What time should I go to bed?
Start from the time you have to get up, not from the time you feel tired. Enter your wake-up time and the calculator lists bedtimes that fit 5 or 6 full cycles plus the minutes you need to fall asleep. For a 7:00 a.m. alarm with 15 minutes to fall asleep, that's 9:45 p.m. or 11:15 p.m.
How long should a nap be?
NIOSH, part of the CDC, describes two options for a nap: a short one with an alarm set 15 to 30 minutes after you lie down, or a long one of about 90 minutes, the predicted end of a sleep cycle. Waking up in between, around an hour in, is when people feel the groggiest. For people on a daytime schedule, NIOSH recommends the short nap.
How do I fix my sleep schedule?
Fix the wake-up time first and keep it every day, weekends included, then let bedtime follow. Move it in small steps, like 15 minutes every few days, instead of an hour at once. The CDC's list of habits helps too: a dark, quiet, cool room, screens away 30 minutes before bed and no caffeine late in the day. If a schedule won't settle no matter what you try, talk to your doctor.
Is there a sleep score?
Not here. Some trackers and apps give a sleep score, and each one calculates it its own way. This calculator doesn't score your sleep. It only plans times from the numbers you enter and the sources listed under the result.
Sources
- Sleep Phases and Stages — National Heart, Lung, and Blood Institute (NIH) — accessed 2026-10-25
- Managing Fatigue During Times of Crisis: Guidance for Nurses, Managers, and Other Healthcare Workers — NIOSH, CDC — accessed 2026-10-25
- Module 8. Day Shift, Relaxation Techniques — NIOSH Work Schedules Training for Nurses, CDC — accessed 2026-10-25
- Module 7. Napping, Nap Duration — NIOSH Work Schedules Training for Nurses, CDC — accessed 2026-10-25
- About Sleep — CDC (Paruthi et al., American Academy of Sleep Medicine) — accessed 2026-10-25