Please tell me if this is right

Depends on how hard you're going at it as well. You can use an elliptical and barely have it moving or you can be pushing at hyper speed and burning tons of cals. Don't most also track distance? Time is great but it doesn't show you effort, whereas you can't really cheat distance as much.

Agreed with the above.

Does your fitbit have a heart rate monitor built in? If so, I would definitely trust that more than an estimate from the internet. 388 sounds way too high.

Faced with competing exercise calorie estimates, and absent persuasive reasons to believe otherwise, I would alway choose to log the lower estimate . . . and eat it back.

StephSuter2508 wrote: »

Trust your fitbit, my fitbit is always lower than the machines estimate, but its based on my heart rate. I noticed that the same class I do every Tuesday, 4 weeks ago I used to burn 480 calories for the hour, this week my fitbit showed only 380 calories because my heart rate has dropped and it takes less effort to do the same class as I am now fitter.

When I enter 60mins of body pump (the class I do) into MFP it says I burn 670 calories for the hour, significantly more than my fitbit says,

As I am trying to lose 40lbs I always go for the lower figure, to be safe

Good news: You don't burn fewer calories doing the same exercise, as you get fitter. That's a commonly-believed myth, and one of the reasons people believe it is that, sadly, heart rate is not really a reliable measure of calorie burn, so heart rate monitors (or trackers that use them) mislead. The devices estimate calories, they don't measure them.

As one loses weight, one will burn slightly fewer calories doing the same the exercise, if the exercise is one that involves a lot of moving one's body through space under direct muscle power (like Zumba or walking/running, say).

At the same body weight, the same exercise (same duration, pace) will burn roughly the same number of calories, irrespective of fitness. It's just physics.

Being fitter makes it feel easier, that's all. Adaptation to exercise (making any given exercise feel and actually be easier) is what fitness is about. It doesn't change the physics.

What we don't know is whether - in your case - the 380 was a more accurate estimate, or the 480. It depends on whether fitter or less-fit you is closer to the fitness of the subjects on which the underlying research was based.

This is an old, but still very good, essay written by an MFP-member fitness professional, explaining why and how heart rate monitors are not completely reliable for estimating exercise calories: https://www.myfitnesspal.com/blog/Azdak/view/the-real-facts-about-hrms-and-calories-what-you-need-to-know-before-purchasing-an-hrm-or-using-one-21472