Sleep Calculator

When to go to bed: times at a glance

With 15 minutes to fall asleep. For other times, use the calculator above.

Wake up at	6 cycles, 9 hours	5 cycles, 7.5 hours	4 cycles, 6 hours
5:00 AM	7:45 PM	9:15 PM	10:45 PM
5:30 AM	8:15 PM	9:45 PM	11:15 PM
6:00 AM	8:45 PM	10:15 PM	11:45 PM
6:30 AM	9:15 PM	10:45 PM	12:15 AM
7:00 AM	9:45 PM	11:15 PM	12:45 AM
7:30 AM	10:15 PM	11:45 PM	1:15 AM
8:00 AM	10:45 PM	12:15 AM	1:45 AM

How the sleep calculator works

Enter when you need to get up or when you go to bed. Starting from the moment you lie down, the calculator first counts the time it takes to fall asleep, 15 minutes by default. Then it adds full sleep cycles of 90 minutes.

An example: you need to get up at 7:00 AM and want 5 cycles of sleep. 15 minutes to fall asleep plus 5 × 90 minutes is 7 hours and 45 minutes. So you go to bed at 11:15 PM.

Below the suggestions, the calculator shows your night as a bar. You can see how the dream periods get longer toward the morning. The calculator runs only in your browser. It saves nothing and sends nothing.

What a sleep calculator can and can't do

Sleep comes in cycles. Each one starts with light sleep, moves into deep sleep and ends with a dream period, REM sleep. Early in the night there is a lot of deep sleep, and toward the morning the dream periods get longer. More on this in When We Dream.

Many sleep calculators promise that you will wake up refreshed at the end of a cycle. The research is less clear. A review of sleep inertia, the grogginess after waking up, found mixed results on whether the sleep stage at awakening matters. A clearer finding: people who are short on sleep wake up groggier.

What the calculator does well: plan your night roughly, with enough hours and matched to your wake-up time. What it can't do: know which stage you are in. Sleep apps and watches can only estimate that, too.

How accurate are the times?

Not to the minute. Ninety minutes is an average. The first cycle often lasts 70 to 100 minutes, later ones 90 to 120. The time it takes to fall asleep also varies from night to night. You can set it in the calculator between 5 and 30 minutes.

Treat the times as estimates. Fifteen minutes earlier or later is just as good. What matters more is getting enough sleep regularly.

How much sleep do you need?

For adults, the American Academy of Sleep Medicine and the Sleep Research Society recommend at least 7 hours a night. The National Sleep Foundation recommends 7 to 9 hours for adults, 7 to 8 from age 65, and 8 to 10 hours for teenagers aged 14 to 17.

That is why the calculator marks 7.5 and 9 hours as "recommended", which is 5 and 6 cycles. Four cycles, or 6 hours, is too little for most people if it happens regularly. You mainly miss the long dream periods in the morning.

The alarm for lucid dreaming

For lucid dreaming, an alarm in the middle of the night isn't a mistake, it's the method. With wake back to bed, you wake up briefly in the second half of the night, stay awake for 10 to 20 minutes, practice a technique like MILD or SSILD and go back to sleep. The long dream periods follow. In the largest field study, this raised the share of nights with a lucid dream from 5 to 16 percent within one week.

The calculator offers two alarm times, exactly like the FinallyLucid app. Both count from the moment you go to bed:

• After 5 hours: in the middle of the night, as in the large field study.
• Early morning: after 6.5 hours, then sleep in. Good for weekends.

If there are fewer than 7 hours between going to bed and getting up, the calculator advises against an alarm night. It also warns you if there isn't a full cycle of sleep left after staying awake. Plan at most two alarm nights a week, and none after a short night. More in Is Lucid Dreaming Dangerous?. Tips for getting back to sleep are in Falling Back Asleep After the Alarm.

Frequently asked questions

What time should I go to bed if I need to wake up at 6 AM?

For 5 cycles at 10:15 PM, for 6 cycles at 8:45 PM. This includes 15 minutes to fall asleep. With 4 cycles it would be 11:45 PM, but that is only 6 hours of sleep.

How long is a sleep cycle?

About 90 minutes on average. The first cycle is often shorter and later ones longer, roughly 70 to 120 minutes overall. In a night with 7 to 8 hours of sleep, you go through about 4 to 6 cycles.

Is it bad to wake up in the middle of a cycle?

No. How groggy you feel afterwards depends on many things, such as how tired you already are. What matters more than the exact moment is getting enough sleep overall.

Why does the calculator assume 15 minutes to fall asleep?

It's a common assumption. If you fall asleep faster or slower, change the value in the calculator.

Which is better: an alarm after 5 hours or early in the morning?

The 5-hour option is the one from the large field study. The morning option disturbs sleep less and suits days off. If you're unsure, start with the morning option on a day off.