Just a note of caution, don't get hung up on BMI. Check out the wiki (
http://en.wikipedia.org/wiki/Body_mass_index) for more details on the problems with it. It really shouldn't be used as an indicator.
I prefer to use other methods to determine how healthy I am, including blood tests for body fat percentages; measurements like waist, hips, chest, etc.; fitness - stamina, weight lifting, etc.
Currently my on scale weight is about +10-15kg more than the top of the range for the "ideal BMI", and while I can definitely afford to lose more fat, I'll never really meet that BMI value. One reason is that I try to gain muscle mass at the same time as losing fat. A couple of years ago, I did a program and lost about 30 kg of fat, but gained about 5 kg of muscle mass in the process. So, now as I'll try to take some more of the remaining fat away, I'll be replacing some of the lost weight with muscle increase instead.
If I was focused on BMI, I'd never succeed, but with more measurable goals, I can see progress (or lapses *sigh*) easier.