With something like that, you really need a heart rate monitor to know for sure.
Otherwise, I would do the method of tracking the minutes spent walking at your estimated speed and then the minutes spent jogging, at your estimated speed.
It's a little bit of a pain, but better than tracking nothing.
When I did the c25k, i had a nike+ ffot pod and the nike app. That calculated the speed and distance for me. But you can also use the endomondo app if you have a smart phone. It's free and uses your phones gps capabilities to track how far you go and how long it takes and will give you a calorie read out for the workout. I have compared it to my heart rate monitor and it actually does pretty good.
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