Height Calculator
Calculate your height percentile using WHO and CDC data, and convert height between centimeters and feet/inches.
Sleep Calculator
Plan a bedtime or wake-up time with sleep cycles, fall-asleep time, age-based sleep guidance, and an estimated phase chart.
Plan your sleep
This calculator estimates schedule timing. If sleep problems are regular, disruptive, or paired with breathing pauses, severe daytime sleepiness, or safety concerns, talk with a healthcare provider.
Estimated sleep phases
Interpret your sleep calculator result
The result is a schedule planning estimate. It uses your chosen wake time or bedtime, a sleep-onset buffer, an age-based sleep cycle estimate, and age-based sleep duration guidance to suggest a practical sleep window.
Inputs that matter most
- Wake-up time or bedtime: the calculator works backward from a wake time or forward from a bedtime.
- Age group: the calculator starts at school age because younger child sleep guidance often includes naps.
- Time to fall asleep: the schedule includes a buffer before the first full sleep cycle starts.
- Sleep amount: choose a cycle count; each option shows estimated sleep time, and a warning appears only when the choice is outside the selected age group's guidance.
- Estimated cycle length: the calculator uses a 90-minute planning estimate based on common adult-like sleep-cycle timing.
Common mistakes
- Treating a bedtime estimate as a medical sleep prescription.
- Forgetting to include the time it usually takes to fall asleep.
- Assuming every sleep cycle is exactly 90 minutes.
- Ignoring sleep quality, frequent awakenings, caffeine timing, shift work, or inconsistent weekends.
When this estimate can be misleading
The estimate can be misleading when sleep is interrupted, when naps make up a large share of total sleep, during shift work, or when a sleep disorder affects rest.
Scenarios to try
- Use wake-up mode when you need to be up for work, school, travel, or an early appointment.
- Use bedtime mode when you know when you can get into bed and want to estimate a reasonable wake time.
- Choose 4 through 9 cycles to see the tradeoff between schedule realism and total sleep.
- Adjust the fall-asleep buffer if you usually need more or less time to drift off.
Next-step utilities
How to use this sleep calculator
Choose whether you know your wake-up time or bedtime, then enter the schedule details you want the calculator to use.
- Choose whether to calculate a bedtime from a wake-up time or a wake time from a bedtime.
- Select the age group closest to the person whose overnight sleep you are planning.
- Set the time it usually takes to fall asleep and choose a sleep cycle count.
- Review the recommended time, recommended sleep range, time asleep, time in bed, and phase timeline.
Sleep Calculator features
- Calculate when to go to bed from a target wake-up time.
- Calculate when to wake up from a planned bedtime.
- Choose from 4 to 9 sleep-cycle amounts, with sleep time shown in each option.
- Account for the time it usually takes to fall asleep.
- Use a cited 90-minute sleep-cycle planning estimate.
- Review age-based sleep duration guidance.
- See time asleep separately from total time in bed.
- View an estimated sleep phase chart with minute-by-minute hover details.
When should I go to bed?
A useful bedtime is usually the latest time that still gives you enough sleep opportunity before your wake-up time.
For many adults, a five-cycle night is a practical starting point because five 90-minute cycles equals 7 hours and 30 minutes asleep. If you also need about 15 minutes to fall asleep, that means roughly 7 hours and 45 minutes in bed. For a 7:00 AM wake-up, that points to about 12:45 AM if you use four cycles, 11:15 PM for five cycles, and 9:45 PM if you use six cycles.
The "right" bedtime is not only a math result. It also depends on sleep quality, consistency, light exposure, caffeine, alcohol, exercise timing, stress, naps, and whether you wake during the night. Use the result as a planning anchor, then adjust based on how rested you feel and whether the schedule is realistic.
How much sleep do I need?
Recommended sleep changes with age. This calculator starts at school age because younger child guidance often includes naps.
For the age groups in this calculator, the CDC lists these daily sleep ranges: school-age children need 9 to 12 hours, teens need 8 to 10 hours, 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. CDC guidance for toddlers and preschoolers includes naps, so this calculator does not turn those totals into one overnight phase chart.
Those ranges are population guidance, not a personalized diagnosis. If you regularly feel sleepy after spending enough time in bed, wake often, snore heavily, gasp or pause breathing during sleep, or have trouble functioning during the day, the schedule math is not enough. A clinician can help evaluate sleep quality and possible sleep disorders.
Sleep calculator methodology and sources
The calculator combines age-based sleep duration guidance with a simple sleep-cycle timing model.
bedtime = wake time - sleep latency - cycles * cycle length
wake time = bedtime + sleep latency + cycles * cycle length
Age-based sleep recommendations are based on CDC sleep guidance. The sleep phase timeline uses the NHLBI description of non-REM and REM sleep, including the note that sleep cycles commonly restart every 80 to 100 minutes and that a typical night often includes four to six cycles.
The calculator starts at age 6 because CDC guidance for toddlers and preschoolers includes naps. A single overnight sleep chart would be a confusing fit for age groups whose recommended total sleep may be split across night sleep and daytime naps.
The phase chart is intentionally simplified. It shows light sleep, deep sleep, REM sleep, and brief wake windows as a visual model. Real sleep architecture changes throughout the night, and clinical sleep staging requires measurements such as eye movement and brain activity.
Brief awake periods are shown as planning estimates, not guaranteed awakenings. Some people wake briefly between sleep cycles, but those moments may be too short to remember.
Sleep calculator FAQ
Is 90 minutes always one sleep cycle?
No. A 90-minute sleep cycle is a planning estimate. NHLBI describes sleep cycles as commonly restarting every 80 to 100 minutes, and real cycle length varies across people and across the same night.
How does the calculator choose sleep cycles?
You choose the sleep cycle count. Each option shows its estimated sleep time, and the calculator warns you when that amount falls below or above the selected age group's sleep guidance.
Why does the phase chart show awake time?
The chart includes brief awake windows as a simplified model. Short awakenings can happen between sleep cycles, but they are not guaranteed and are often not remembered.
Why does the calculator start at age 6?
CDC guidance for toddlers and preschoolers includes naps. This calculator focuses on one main overnight sleep window, so it starts with school-age children where a night-only schedule is a clearer fit.
Can this diagnose a sleep problem?
No. This is a timing and planning tool. Talk with a healthcare provider if you regularly have trouble sleeping, wake often, feel very sleepy during the day, or suspect a sleep disorder.
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