Calculating Your Perfect Bedtime and Sleep Efficiency

couple sleeping

Most people have what I call a “socially determined wake-up time” – some type of social, family or financial commitment that requires them to wake up at a particular time. It may be to take out the dog, feed the cat, make sure a child is ready for school, or avoid being late to work. Whatever it is, it is the time you have to be up and out of bed. And because of these needs (some of which aren’t even your own), the time you wake up is somewhat out of your control.

However, the time you go to bed is usually something you can control. Knowing the right time to go bed – based on the number and length of normal sleep cycles – can really increase your chance of getting the quantity of sleep you need and the quality of sleep as well.

The goal is to wake up naturally just about the time your alarm is set for that wake-up time. You already know what time you need to wake up, so you have one piece of the Perfect Bedtime Formula, which is a simple four-step process.

1. The average sleep cycle is approximately 90 minutes long.

2. We know that the average person has 5 sleep cycles per night.

3. Multiply 90 minutes by 5 sleep cycles per night for 450 minutes or 7.5 hours of sleep.

4. Then count backwards from your wake-up time 7.5 hours and you have a starting point for your bedtime.

Example: You need to wake up to get ready for work at 6:30 a.m. Counting backwards 7.5 hours, your lights-out time is 11:00 p.m. Lights out – in bed ready for sleep.

Notice I said starting point. If your lights go out at the time you calculate (your bedtime) and you sleep until about 5 to 10 minutes before your alarm goes off in the morning, congratulations! You have found your bedtime. If you wake up an hour before your alarm goes off in the morning, then you can try going to bed a bit later.

If, however, after one week you still need an alarm, then move your bedtime back in 15-minute increments, until you are waking just before your alarm. Remember, the goal here is to wake naturally before your alarm.

Keep in mind, it can be as difficult to go to bed on time as it can be to wake up on time. Have you ever promised yourself you’d go to bed early, and suddenly realized that you are hours past your well-intended bedtime? Use the alarm in your bedroom to help with your bedtime – set that alarm 30 minutes before your bedtime! This forces you to walk into your bedroom and is a cue to remind you it is time to get ready for bed.

Measure Your Sleep Efficiency
In sleep science, we use many different calculations to teach us how people sleep. But sleep is not just a quantity issue but also a quality issue as well. While it is fairly simple to measure how many minutes a person spends asleep, it is often not so easy to measure the quality of that sleep.

When looking at sleep quality, we often try to see how much of certain sleep stages a person gets. Stages 1 and 2 are known to be the light stages of sleep. We know that Stages 3 and 4 are the physically restorative sleep. These are the stages when the “wake up and feel physically ready to meet the day” sleep occur. And we know that REM sleep (Rapid Eye Movement) is the mentally restorative sleep – this is the sleep that helps your memory, and lifts the fogginess of dreamland.

In the past the only way to measure the amounts of these stages was to attach electrodes to a person’s head, monitor their brainwaves all night long, and calculate the percentages of each stage of sleep. But there is another, simpler way that everyone can calculate their sleep efficiency at home.

It has been well documented that the sleep process works in a particular pattern. When you sleep, you go from wake to Stage 1 to Stage 2, to Stage 3 and 4, back to Stage 2 and into REM sleep. This cycle takes 90 minutes and you should have a minimum of 5 cycles throughout the night (see the bedtime calculation above). But, if you are woken up in the middle of a cycle, your brain goes back to the beginning and starts the entire process over again! It is like having to start the race back at the starting gates, even if you are pretty close to the finish line. The fewer interruptions you have to your sleep, the better your sleep quality (since fewer interruptions allow you to complete an entire sleep cycle).

Take a look at the amount of time you spend in bed asleep (minus all the awakenings you may have and how long it takes you to fall asleep), and divide it by the total time you spend in bed, you will get an estimate of the overall percentage of how efficiently you sleep! While it is not exactly the same as monitoring your brainwaves, it is still a good measure of sleep quality. In the sleep science world, we like to see this number above 85%. We consider 85% as normal and really good sleep efficiency is above 90%.

For example: You go to bed at 11 p.m. It takes you 25 minutes to fall asleep, and you wake up 3 times for 5 minutes, 15 minutes and 5 minutes again. You wake for the day at 6 a.m.

Here is how to calculate an estimate of your sleep efficiency:

Sleep Efficiency Calculator
Total Sleep Time = 7 hours (420 minutes)

Minus time to fall asleep = 25 minutes

Minus time awakened= 25 minutes (5 minutes + 15 minutes +5 minutes)

Total time asleep = 6 hours and 10 minutes (370 minutes)

Now divide 370 minutes /420 minutes = 88%

While 88% is within the normal range, there is still room for improvement!

  • Try sleeping longer – go to bed earlier.
  • What is waking you during the night? Could your room be darker, more quiet?
  • Are you uncomfortable – time for a new mattress or pillow?

Sweet dreams,

Michael J. Breus, PhD
The Sleep Doctor™