Heart rate monitor accuracy

1) Height, weight, vo2 max (some HRM's take this into account, some don't) will all factor into how many calories you burn
2) You want to deduct your BMR calories from whatever calculation the HRM gives. For example:

According to my fitbit I burn approx. 16 calories every 15mins of no activity.
So in an hour with no activity that would be 64 calories.
If my HRM gives me a 700 calorie burn, I should only log 636.
(Personal preference of mine is to deduct 20% to be on the safe side.)

3) HRM's are less accurate for anything outside of steady state cardio. See thread below:

http://www.myfitnesspal.com/topics/show/1044313-this-is-why-hrms-have-limited-use-for-tracking-calories?hl=accuracy+of+HRM&page=1#posts-16031917

Totally depends on all the details as above including how fit you are. Also any medications. For example I'm on Beta Blockers for Blood pressure and migraine so my heart rate will NEVER get that high
Some people can get higher than others. If you don't eat them back don't stress just use it as a guide.

I'm wondering the same thing. I have a polar FT4 and it was suggested to me that I should wear it for a 24 hour period to see what calories I burn a day. I have 2 minutes left and it's reading at 4018 calories. That number seems high to me since it doesn't include any exercise . Just been sitting at home with a 3 year old, doing housework and a trip to the shops to get dinner.
My resting heart rate according to HRM is 82 and walking to the bathroom my heart rate was at 102.

HRM's are not accurate for calorie burns when the heart rate is so low. They are only good for steady state cardio with elevated heart rate. Directly from the thread I listed above:

Once you leave the realm of steady-state aerobic exercise, however, accuracy of HRMs deteriorates rapidly.

How do you calculate BMR?

I wasn't eating all of the calories back. Actually I think I sabotaged myself for a few months because I hadn't been eating back any! Oops!

There's a BMR calculator right here on the website (not sure about the app). Go to the APPS menu, then click on BMR on the submenu and once you confirm your current stats are prefilled correctly, click calculate. Once you get that number, you can divide by 24 then divide by 60 and that'll give you the approximate # of calories you burn per minute.

For instance, my BMR is 1500 so that's about 1 calorie per minute.

I consistently burn between 500 and 800 calories at Zumba, depending on my gusto and the instructor's song choice. It certainly seems conceivable to get above 1000 depending on your weight, height, etc. When I initially started committing to fitness awhile back I always exceeded 800 calories, sometimes pushing 1000.

I have a Polar FT4 with my age, height, weight, etc. factored. Almost every workout with a consistently elevated heart rate amounts to approx. 10 calories/minute, for me. It's sort of uncanny.