Lessara, you should use your actual weight. Carrying around the extra fat does take energy and resources. And no, I think the 10 - 12 number takes into account that everyone is different and BMR is 60-70% of caloric intake (and not say, a 75% constant); it's not like "You're 10% overweight, so multiply by 10" etc.

It is all approximation, of course. Unless you go in and have some serious testing done

Nat