Body Mass Index a.k.a BMI is an indicator of your body weight according to your height. BMI helps you determine if your body weight is in a healthy range or you are overweight. Your body mass index (BMI) can help you understand if you need to lose weight, maintain or gain weight.
The point to note is that BMI is just an indicator of weight and does not take into account your muscle mass or fat percentage. Your weight comprises of muscle mass, fat mass and water mass. You can have a low muscle mass but your BMI might still show you in the healthy range.
I suggest you to use BMI as an indicator of being overweight or not. If you are in acceptable range of BMI, check your muscle mass and fat mass with an advanced BMI machine.
The formula for calculating body mass index (BMI) is BMI = Body weight(kg)/Height^2 (m)
This BMI calculation is applicable to most of the adults 18-65years old. BMI between 18.5-25 is a healthy range. If you are above 25, you need to lose weight.