P90

Welcome to the P90X club! My husband and I have done 2 rounds and really love the program! Your best bet is to get a heart rate monitor. How much you burn will vary dramatically from someone else depending on things like age, weight, intensity of your workouts, etc.

It should also be mentioned that how much you burn will change as you progress, particularly if you lose weight. It also varies from workout to workout so the best way to keep track is to get a HRM. You won't regret it.

some will estimate your calories, some dont. there are web calculators for calories by heart rate. mine just gives me avg HR and time, I calc on the web.

Well, I think the HRM is accurate enough.
here is a calculator I use. http://www.braydenwm.com/calburn.htm

I ran with a garmin that had a HRM and it basically calculates the same as the web page, they both work off of the same basic formula. it just saved more data points than my el cheapo that only gives me one total avg beats/workout.

I think to get any more accurate, you would need something like a bodybugg.

Another option you may want to look at is the Polar HRM most of the newer models come with a watch and a coded HRM strap that goes around your chest. the beauty of this is you can find a basic one that does HR and calories Burned ( i found one on sale for $40 (Polar FT4) it also stores your workout data for a couple weeks at a time. Also if you ever decide to go to the gym as well and your gym has Polar equipment... put your HRM strap on and the machine will automatically detect your hrm and use it... its very cool!