What time should you go to bed? Calculate your bedtime and wake-up time
Estimate a bedtime or wake-up time using scenarios of 7, 8 and 9 hours of sleep. No calculation predicts when your cycles will end.
Short answer
To get up at 7 am with 8 hours of sleep and 15 minutes to fall asleep, go to bed around 10:45 pm. An adult needs at least 7 hours. Sleep cycles vary from person to person and night to night: no calculation guarantees you will wake during light sleep.
Calculator
Validated inputsYour settings
Bedtime scenarios
Wake-up scenarios
How to read these results
The scenarios allow for 7, 8 or 9 hours of sleep, plus the time it takes you to fall asleep. Nighttime awakenings are not taken into account.
The 15 minutes by default are an interface value to adjust to your observations, not a universal duration.
The times do not predict your cycles or whether you will wake during light sleep. Compare the available time with how you feel and your alertness during the day.
Sleep cycles and stages vary throughout the night. This tool does not measure them.
To organise your schedule, keep a consistent bedtime (even on weekends) and a exposure to natural light upon waking.
To learn more, explore our articles: Sleep inertia • Deep sleep • Glycine & sleep
What the tool measures
Set aside time for sleep
The NHLBI generally indicates 7 to 9 hours of sleep for adults. Individual needs and actual time asleep vary.
Sleep alternates between stages over variable cycles. This planner does not measure these stages or infer them from bedtime. It only organizes the available time.
Interpreting the result
Interpret without overpromising
The 7, 8 and 9-hour scenarios are reference points to compare with how you feel and your constraints. The time to fall asleep you enter is added to the planned sleep duration. Nighttime awakenings are not included.
For a 7 am wake-up, 8 hours of sleep and 15 min to fall asleep, the calculated bedtime is 10:45 pm. This reference point does not guarantee that you will fall asleep or feel recovered.
Calculation and assumptions
Methodology
- Estimated bedtime = wake-up time − scenario sleep duration − time to fall asleep.
- Estimated wake-up time = bedtime + time to fall asleep + scenario duration.
- Calculations wrap back into the 0 to 24 h range when the time crosses midnight.
The default 15 min is an adjustable interface value, not a universal median. The model uses sleep durations, not multiples of a 90 min cycle.
Sources consulted
Sources
- NHLBI, How Sleep Works: How Much Sleep Is Enough?
Duration benchmarks by age, particularly for adults.
- NHLBI, How Sleep Works: Sleep Phases and Stages
Description of sleep stages and cycle variability, which this calculator cannot predict.
Scope of validity
Limitations to know
The calculation does not account for nighttime awakenings, sleep disorders, treatments or shift-work constraints. It does not guarantee that you will wake up during light sleep. Persistent difficulties, daytime sleepiness or observed pauses in breathing warrant professional advice. The model is intended to help organize an adult's schedule, not to meet children's needs.
Frequently asked questions
Before using the result
Can I predict the end of a cycle?
No. Cycles and stages vary. A bedtime alone is not enough to predict waking during light sleep.
Why 7, 8 and 9 hours?
These are scenarios based on the general guideline of 7 to 9 hours for adults. They do not establish your individual needs.
Does taking 15 minutes to fall asleep apply to everyone?
No. It is a default value to adjust based on your observations. Nighttime awakenings are not included.