Originally Posted by
Acopella 95 Is it? I hope that's right otherwise I gonna be so disappointed as it keeps drain my battery quite fast even not using it.
Yes, it is definitely an estimation based on your usage for that day. My Pixel 2 does the same thing. Sometimes it'll say I have a day and six hours left of use; and other times, when I'm using it more heavily, it'll say 22 hours or something. Don't worry!
Also, as orangecroc above me stated, it'll take a little while/some charging cycles for the phone to become more intuitive and to perform at its maximum with regards to battery.