Is there one on MYPLAN? If there is could you tell me how to use it? *dang newbies!*

No, it doesn't have a BMI calculator.

It was dropped in preference to body fat calculation, as a more accurate measure, since BMI penalizes those with more muscles, and rewards weight loss, regardless of fat loss or muscle loss.

Wa'il

Here's the one I use:
http://www.johnhustedmd.com/bmi.htm

Just enter your height and weight and hit calculate. There is a table which indicates what the results mean. As Tamarian said, BMI doesn't take into account muscle mass, so you have to take the result with a grain of salt. I found it helpful as a starting out point, and will re-evaluate when I get closer to my goal weight.