What time to go to bed for a 5am alarm, without a calculator

Your alarm is set for 5am, for an early shift or a gym session before work. You want to know what time to turn the light off tonight so that alarm wakes a rested person rather than someone who stops it in their sleep.

Bedtime calculators answer this with 90-minute sleep cycles. You do not need one. You need two numbers you already have, and the subtraction takes a minute.

Start from how much sleep you need

The first number is your sleep need. In 2015 a panel convened by the National Sleep Foundation, led by Max Hirshkowitz, published its recommendations in the journal Sleep Health. For adults aged 18 to 64 the panel recommended 7 to 9 hours a night. For adults 65 and over it recommended 7 to 8. For teenagers aged 14 to 17 it recommended 8 to 10. The panel judged 6 hours "may be appropriate" for some adults, and we read that as a floor a few people can stand on, not a target.

The range is two hours wide, and against a 5am alarm that is the gap between a 9:40pm bedtime and a 7:40pm one. You need your own number.

The best measure most people have is the end of a holiday. On the first nights you sleep long because you are repaying the weeks before, so ignore those. By the fourth or fifth night without an alarm, the hours you sleep are close to what your body wants. If you have never had a week like that, use 8 and adjust after a fortnight. Waking before the alarm and feeling fine means you can trim. Feeling slow all morning means you cannot.

Add the time it takes you to fall asleep

The second number is the gap between lights out and sleep. A bedtime is when you stop, not when sleep starts, and the two are rarely the same. Use your own gap if you know it, and 20 minutes if you do not.

One opinion of ours. If you fall asleep within a minute or two of lying down most nights, treat that as a sign you are already short on sleep rather than as a talent.

The bedtimes, counted back

With 20 minutes to fall asleep, here is when the light goes off for seven, eight, and nine hours of sleep.

• Alarm at 4:30. Lights out at 9:10pm for seven hours, 8:10pm for eight, 7:10pm for nine.
• Alarm at 5:00. Lights out at 9:40pm for seven hours, 8:40pm for eight, 7:40pm for nine.
• Alarm at 5:30. Lights out at 10:10pm for seven hours, 9:10pm for eight, 8:10pm for nine.
• Alarm at 6:00. Lights out at 10:40pm for seven hours, 9:40pm for eight, 8:40pm for nine.

Read the 5:00 line once and the problem with a 5am alarm shows itself. Eight hours of sleep before it means the light goes off at 8:40pm. For an adult with a job, dinner to cook, and anyone else in the house to talk to, that bedtime decides the shape of the whole evening. What you cannot do is set the alarm for 5:00, turn the light off at 11:00, and expect the morning to feel like anything other than six hours of sleep, because that is what it was.

If the number the list gives you is one you will not keep, move the alarm rather than keeping a bedtime you will miss. A 5:30 alarm you wake for beats a 5:00 alarm you stop in your sleep.

Skip the 90-minute cycle rule

Bedtime calculators promise to land your alarm between sleep cycles so you wake at a light point and feel sharper. The arithmetic assumes every cycle lasts 90 minutes. It does not. In their overview of normal human sleep in Principles and Practice of Sleep Medicine, Mary Carskadon and William Dement put the average cycle at roughly 90 to 110 minutes, and the cycles change length across the night. Cycle length also differs from person to person.

So an alarm placed by counting 90-minute blocks from lights out rests on three unknowns. You do not know when you fell asleep to the minute, you do not know your cycle length, and you do not know how tonight's cycles will run.

The rule does one thing we dislike. It makes 6 hours look like a sensible choice because 6 hours is "four cycles" and 7 hours is "four and a half". Total sleep decides how you feel tomorrow, and you cannot schedule a cycle boundary.

An early alarm needs a harder stop than a late one

The subtraction tells you where bedtime belongs. It does not make 5am feel any less like the middle of the night, and on the mornings you missed bedtime by an hour, the alarm lands on a body short on sleep.

Nobody else needs you up at 5, and a skipped run costs nothing you can see that morning. That is why an early workout alarm fails more often than a work alarm does.

This is where we think the dismissal has to involve your body, not your thumb. BarLock rings as an AlarmKit system alarm, so it sounds on the Lock Screen and through silent mode like the built-in iPhone alarm, and it ends only when you scan a barcode or QR code you chose the night before. Put the code on the kit bag by the door or the kettle, and the alarm ends in a room with your shoes in it. The Lock Window keeps 11pm you from pushing the alarm to 7:00 on behalf of 5am you. Backup Alerts ring again if you tap Stop before the scan. The Wake-Up Check asks you to confirm you are still up a few minutes after the scan, which covers the walk back to a bed that is still warm at 5:08. The no-snooze routine page has the setup step by step, and the use case library has routines for gym mornings and early shifts.

Moving bedtime two hours earlier takes more than deciding to

You can set the alarm for 5:00 tonight. You cannot set yourself to be asleep at 9:00 tonight if you fell asleep at 11:30 last night. Bedtime is the end of the night you earn, as we argued in the post on fixed wake times, and the wake time is the end that moves the clock.

So move the alarm first and let bedtime follow. Hold the 5am wake, get light soon after it, and sleep pressure will pull the evening earlier over a week or two. Keep the wake time within an hour on days off, because a 9am Saturday undoes the week.

Expect the first week to be short on sleep. A harder alarm gets you up through it without making it feel good.

If weeks of a held wake time and morning light still leave you lying awake until midnight, your clock may sit late enough that arithmetic cannot reach it, and that is a question for a clinician rather than a list of bedtimes.