The table below shows the BMI scale:
From the chart above, we see that healthy BMI falls in the range between 18.5 and 24.9. People whose BMI test value falls in this range are considered healthy based on their weight and height. A healthy BMI actually covers a wide range of weights. For example, if you are 5'8", you can weigh anywhere between 122 pounds and 164 pounds and be considered healthy.
People who are in the overweight (25 - 29.9) and obese (>= 30) scales are considered to have too much body fat. According to the CDC, 63% of U.S. adults are either overweight or obese based on BMI in 2007. People who are in the underweight (<= 18.5) scale, on the other hand, are considered to have too little body fat.
Keep in mind that BMI index test is only one measure of your health. Many other factors also play an important role in your health. As such, having a healthy BMI does not mean that your body is in perfect health.