With 39 min of screen time, I'm at 87% and it's predicting 7 more hours. I'm thinking that cell signal is the culprit, but even my note 3 wasn't this bad. I usually got almost a full day from it.
The battery prediction looks at how you have used the phone since the last full charge, and assumes that you will continue to use it that way for the rest of the day - so if you took it off the charger at 100% and then, spent 40 minutes browsing the web or playing games etc, and 20 minutes on standby, the phone will assume that you will continue to do so, and gives you an estimate based on that usage scenario. If you keep the phone on standby after that for 3 hours, the remaining battery life estimate will adjust accordingly.
For example, I charged my phone to 100% at about 11pm last night, and took it off the charger, turned off data/Wifi, and left it untouched overnight. This morning, it shows me 96% charge, and estimates that I have several days of battery life left. During the day, because I'll actually be using the phone, the "time remaining" will adjust according to my actual usage.
So, in summary, look at how much battery you are left with at the end of the day, and see if that makes sense. If you think that your battery isn't lasting at long as your other devices, then look at battery usage and see what's draining your battery