Bedtime Calculator
Bedtime by age
Sleep need is set by age band. The cycle count follows from the target, not the other way round.
For children under 6, the total includes naps. Subtract nap time from the night target rather than stacking both.
Most bedtime advice starts with a number of hours and stops there. That leaves out the two things that actually decide your bedtime: how much sleep someone your age needs, and where the nearest cycle boundary falls. The calculator above uses both.
How the bedtime window works
Your sleep need is a range, not a point. An adult needs 7 to 9 hours, which means there is a two-hour bedtime window rather than one correct time. The earlier end of the window is the one to aim at when you are catching up, ill, training hard, or under load. The later end is the one you can hold on a normal week.
Inside that window, the cycle-aligned bedtime is the option that puts your alarm at the end of a 90-minute cycle. It is not more important than getting enough total sleep, but when two bedtimes give you a similar total, take the cycle-aligned one.
Set the wake-up time first
This is the part people get backwards. Bedtime drifts because it depends on the evening, which is the least controllable part of the day. Wake-up time is fixed by work, school, or a train. Anchor the schedule to the fixed end and let the bedtime follow.
A fixed wake-up time also does more for your body clock than a fixed bedtime does. Morning light at a consistent time is the strongest signal your circadian system gets. Getting up at the same time every day, including weekends, is what makes the bedtime start to feel natural instead of enforced.
What to do when the bedtime does not stick
- You lie awake for 30+ minutes. Your bedtime is ahead of your body clock. Move it later by 30 minutes, then walk it back in 15-minute steps over a couple of weeks.
- You fall asleep instantly every night. That sounds good but usually means you are sleep-deprived. Healthy sleep onset takes 10 to 20 minutes. Move bedtime earlier.
- You wake at 3 AM and stay awake. Look at alcohol and at time in bed. Both fragment the second half of the night. The sleep efficiency calculator quantifies how much of your night this costs.
- Weekends undo the week. Cap the weekend shift at one hour. Two hours is a time zone.
Bedtimes by age at a 7:00 AM wake-up
| Age | Sleep needed | Bedtime window |
|---|---|---|
| 3-5 years | 10-13 hours | 5:45 PM - 8:45 PM |
| 6-12 years | 9-12 hours | 6:45 PM - 9:45 PM |
| 13-18 years | 8-10 hours | 8:45 PM - 10:45 PM |
| 18-64 years | 7-9 hours | 9:45 PM - 11:45 PM |
| 65+ years | 7-8 hours | 10:45 PM - 11:45 PM |
Windows include ~15 minutes to fall asleep. For teenagers the biology genuinely pushes bedtime later, so an 8:45 PM bedtime is unrealistic for most; aim at the late end and protect the wake time.
Next: build the rest of the evening around this with the sleep schedule calculator, or check the total you are actually getting with the hours of sleep calculator.