How do you guestimate how many calories??

I use sparkpeople too. I've read quite a few articles about how these apps probably overestimate calories burned, so I also just find something similar and then enter less time. For example, if I do Zumba for an hour, I might find a "dance aerobics" on the app and enter 45 minutes instead of the full 60. In general I try to overestimate calories and underestimate exercise to keep myself honest.