You've gotten some good advice; an HRM will give you the most accurate estimate, but in the end, they are *all* estimates. Unless you're in a lab hooked up to monitors and machines, you're never going to know the exact amount you're burning,g and that's okay. You will always have some room for error, though. Your body isn't a calculator, and as long as you're giving it the best try, you'll be fine.
Don't worry about your daily calorie burn; your range here takes daily activity including housework and such into account already. Trying to count that as well is just double-counting! Don't worry about underestimating. If you are weighing and measuring, you can reasonably expect to be fairly accurate.
This isn't about perfection. With the elliptical, the burn will likely be less than running, as it's a low-impact exercise. With resistance, it gets wonky. That's where the HRM will be more helpful for you, for exercises not as frequently studied.
90% of us here go with rough estimates, and it works. :)
Writer, mother, wife, and breadwinner. I love to run, but running doesn't love me, so I'm switching to my low-impact bike.
I'm not pregnant, just fat: My blog. fatnotpregnant.blogspot.com/
| current weight: 186.4