There are two likely explanations for seeing sleep durations that are shorter than what is displayed in your other apps.
1. You experience one or more periods of being awake for 40 or more minutes during the night/your designated sleep time.
2. There is data missing from your account.
You may be asking “Why does it matter if I wake up during my sleep time?” To answer this, we must first understand the difference between main sleep and additional sleep.
Consider your main sleep as your longest asleep period with any awake intervals being less than 40 minutes. Confused? Example time!
Meet Joe. Each night Joe falls asleep at 10:00 p.m., wakes to answer the call of nature at 12:15 a.m. and is asleep again at 12:30 a.m. before waking to start his day at 6:00 a.m.
Two sleep periods can be identified for Joe:
Sleep one - 10:00 p.m. to 12:15 a.m. (2 hours 15 minutes)
Sleep two - 12:30 a.m. to 6:00 a.m. (5 hours 30 minutes)
Even though Joe didn’t sleep through the night uninterrupted, the interval between the two periods was less than 40 minutes. Because of this, these two periods can be combined to represent Joe’s main sleep. When Joe opens our app he will see a sleep duration of 7 hours and 45 minutes displayed on his sleep graph.
Any sleep period that is shorter than your main sleep and occurs over 40 minutes before or after your main sleep is considered as additional sleep.
Meet Josie. Each night Josie falls asleep at 9:00 p.m., wakes at midnight to watch her favourite late-night talk show, then falls back asleep at 1:00 a.m. before waking at 7:00 a.m. to start her day.
Two sleep periods can be identified for Josie:
Sleep one - 9:00 p.m. to 12:00 midnight (3 hours 0 minutes)
Sleep two - 1:15 a.m. to 7:00 a.m. (5 hours 45 minutes)
Josie’s total sleep duration is 8 hours and 45 minutes, however because there was an interval of more than 40 minutes separating the two periods, only the longest sleep period will be classified as her main sleep.
The shorter sleep period will be classified as an additional sleep period - and will not be included in our analysis. So, when Josie opens our app, she will see a sleep duration of 5 hours and 45 minutes displayed on her graph.
Why don’t we include additional sleep in our analysis?
There is a HUGE volume of research that looks at the way sleep duration affects us physically and mentally. But get this: ALL of these studies take into account a person’s main sleep only. We have a responsibility to give our users evidence-based ratings and advice, which is why we only use main sleep in our analysis too.
Disrupted sleep, like Josie’s, has a different impact on the body than if she had slept for the same amount of time without the long interruption. Need an example? Imagine you have a terrible headache and you need pain relief ASAP! Would you take two aspirins now? Or would you take half an aspirin every hour for the next four hours? It's the same amount, but the timing makes a big difference to how you feel.
If you’re concerned there may be a data error, there’s no need to sit in uncertainty – just drop us a line and include a few screenshots!