The Body Mass Index is a statistical measurement using your weight and height.
Due to its ease of measurement and calculation, it is the most widely used diagnostic tool to identify weight problem within a population.
Even though BMI does not actually measure the percentage of body fat, which is one of the most important elements of long term weight loss, it is a good place to start.
BMI is meant to be used as a simple means of classifying sedentary individuals with an average body composition.
It is an alternative for direct measures of body fat.
But for the best assessment to determine if your current body fat is a health risk, other methods are a lot more accurate.
One of the best is skinfold thickness measurements which gives you the percentage of your current body fat, and for long term weight loss this is what you must work on lowering.
There are many other ways of calculating ideal weight, but noneof them can come close to using skinfold measurements.
When losing unwanted body fat is your major goal, then this is what you have to keep your eye on, if you want long term results.