MFP vs Treadmil question

destes557

So my question is this. I use a treadmil at the gym where I input my age and weight before working out. After I run and walk it tells me how many calories I burned doing the cardio for that day however once I put in my times on MFP it is lower than what the treadmil said. What is the reason behind this and which one do I go by???