How to calculate calories burned, but you must have a HRM to get your average HR

The following equation from the Journal of Sports Sciences calculates the calorie expenditure for women: Calories = [(0.074 x Age) + (0.4472 x Heart Rate) -- (0.05741 x Weight) -- 20.4022] x Time / 4.184. Men use the following equation: Calories = [(0.2017 x Age) + (0.6309 x Heart Rate) -- (0.09036 x Weight) -- 55.0969] x Time / 4.184.

Courtesy of Livestrong.com http://www.livestrong.com/article/228774-calories-burned-from-high-intensity-interval-training/

I used this formula to calculate my calories burned at an average heart rate of 179 and a 40 minute workout. It comes out to 526 calories for my workout today. I have a HRM with a chest strap but it doesn't calculate calories burned. It's an F1 Polar HRM which I got a long time ago for spinning classes but I use it now for my Insanity workouts because it's "High Intensity Interval Training!" I just ordered the S7 HRM from Walmart and it was $29. I'm just using it to get the calories burned since I tried a pedometer and that didn't read accurately. It said I only burned 80 calories for 2 miles and that's not accurate for doing the Insanity workouts!