Samsung Health app, how accurate is the calories for steps? and how do i sync it with myfitnesspal?

Hi.

I'm planing to have a kcal surplus of 2-3-400 kcal a day, but to do this I need to know pretty accurate how many kcal i use.
In work I some days sit at the computer all day, but other days i am moving all the time, so it is very variable.
I think this can be counted by using a pedometer (step counter), but how accurat is this? I know the step-counter og my galaxy S7 is very good, it count correct, at least steps, don't know about kcal, do you? (it also count speed and so on)
Examples:
today: 19450 steps, 15,41km, 831kcal,
yesterday: 16771 steps,13,27km ,711 kcal
day before: 3045 steps, 2,41km, 133 kcal

I also som days ago had 38706 steps and 38,69km, 2652 kcal (but this was dancing at a rave, so maybe not accurat)


anyway, hvis is what i want no know at this time:
- can i trust s health? or is there any better apps?
this? https://www.myfitnesspal.com/apps/show/4
- how can i sync it?