Deep Sleep Percentage

So my deep sleep percentage has been around 40-45ish. The average for the US seems to be 50ish according to SAA data. I shared that with a friend of mine that has a Fitbit. He was surprised to hear that and said that his % is around 20-25, and that that’s around normal. I got curious and looked around the internet, and pretty much all info says that normal deep sleep is about 10-25% (example: https://www.healthline.com/health/how-much-deep-sleep-do-you-need). So how come SAA’s deep shows as much higher than what should be typical? I’m sure there is a good explanation :slight_smile:

My guess is that it has to do with there being 2 stages of “light” sleep, one much deeper than the other. So, it’s a judgement call as to where to put stage 2 sleep. True Delta wave sleep is relatively brief, but including stage 2 sleep in “deep” gives people a better picture of their night, I think.

Perhaps those charts will help.

In other words, without eeg sensors, it’s a guessing game between stages 2 and 3. But in both, the sleeper has fallen into a deeper sleep than stage 1 light sleep. To attempt a guess at true Delta wave sleep is perhaps disingenuous, whereas SaA includes both theta wave and delta wave sleep in the deep rather than light sleep category. In both cases, HR and body temperature drop and brain waves fundamentally change.

I thought the answer would be something like this. It would be nice if the devs could chime in as well though.

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Yes, I also would be interested in their point of view.