Body Mass Index (BMI) Calculator – Risks Involved Being Overweight, Underweight

Introduction 

The BMI (Body Mass Index) is the current metric for defining anthropometric height/weight characteristics in adults and categorising them into groups. 

The most common interpretation of BMI is that it represents an index of an individual's fatness. 

It is also widely used as a risk factor for the development or prevalence of various health issues.
 

What is BMI?

Body Mass Index (BMI) is a measurement of a person's weight in relation to their height. It is an indirect indicator of a person's total body fat than a direct measurement.

BMI is calculated from an individual's Weight and height. It is a fast, easy measure that categorizes people into a variety of weight categories, ranging from underweight to obese. Healthcare professionals frequently use BMI as the primary measure for assessing the risk of weight-related health problems.

BMI Formula 

BMI is a weight-for-height measurement calculated as weight in kilogrammes divided by height in metres squared (Kg/m2).

BMI = Weight (Kg) ÷ [Height (m)]2

The formula for calculating BMI varies depending on the system of measurement used:

●Metric System:
●BMI = Weight (kg) / [Height (m)]²
●Imperial System:
●BMI = [Weight (lbs) / Height (inches)²] × 703

Significance of the BMI Calculator

• A BMI calculator (body mass index) is a tool for assessing weight status and many health risks. It is often used in applications such as weight management.
• BMI helps determine the risk of developing some health conditions, like heart disease, type 2 diabetes, high blood pressure, etc., in your body.  
• A doctor uses your BMI to help with preventative care, like diet counselling, diabetes screening, exercise counselling, and thyroid screening. 
• The BMI calculator is used in surgical clinics, as it helps determine recovery time and the risks of complications. 
• The health of populations can be assessed using BMI charts, as they can point out poor diet, activity levels, or stress. 
• You can get this BMI calculator through many mobile websites.

How does BMI classify weight? 

The Adult BMI Calculator helps them determine which category they are in. Let’s discuss BMI's weight status. 

• Individuals with a BMI less than 18.5 come under the Underweight status.
• People with a BMI between 18.5 and 24.9 have a healthy weight. 
• People with a BMI between 25.0 and 29.9 are considered overweight. 
• Individuals having a BMI of 30.0 and above have obesity.
• The weight status of a person may help determine their health risks.
   

BMI table for adults 

Adults aged 20 and up can use BMI to analyse their category. BMI is calculated using standard weight status categories that are the same for men and women of all ages.

The following is the BMI categorisation for the Asian-pacific population as suggested by World Health Organisation (WHO).

BMI < 18.5 Kg/m2 

BMI less than 18.5 Kg/m2 indicates a low body fat percentage and a lean body mass. A person with this BMI is regarded as underweight. 

If the BMI and body weight are low, one should consider gaining weight through good diet and exercise habits to increase muscle mass.

BMI between 18.5 - 22.9 Kg/m2

This BMI represents an ideal, healthy amount of body fat. A healthy BMI is associated with the longest life expectancy and the lowest incidence of severe illness. 

Coincidentally, it appears that this ratio is what many people consider to be the most elegant.

BMI between 23 - 24.9 Kg/m2

BMI between 23 - 24.9 Kg/m2 is regarded as an acceptable range and is linked to good health. But these individuals have to maintain or lose their weight to not fall under the obese category, which makes them prone to lifestyle diseases.

BMI 25 - 29.9 Kg/m2 

People under the obesity grade I category should work to lose weight through diet and exercise. At their current weight, they are predisposed to several illnesses.

BMI greater than 30 Kg/m2

This BMI signifies an unhealthy state, and people with this BMI are classified as Obesity grade II. 

Surplus weight places a person at risk for Diabetes, heart disease, high blood pressure and some cancers. Striving to lose weight by changing their diet and exercise helps them become normal.

To calculate BMI manually, do the following:

Measure Your Weight:
Use a good measuring scale to measure your Weight in kilograms (kg) or pounds (lbs).
Measure Your Height:
Take an accurate measure of your height in meters (m) or inches (in).
Apply the Formula:
Insert your Weight and height into the correct formula to find your BMI.

Example Calculation:
Consider that someone weighs 70 kg and stands 1.75 meters tall. The BMI can be determined through the following:
BMI = 70 / (1.75 × 1.75) = 22.86

Thus, the person’s BMI is 22.86, which falls within the "normal weight" category.

BMI table for children and teens (age below 20) 

The interpretation of BMI is unique for children and teenagers, depending on their age and gender.

BMI Percentile for Child and Teen provides BMI and the corresponding BMI-for-age percentile based on CDC growth charts for children and teens aged 2 to 19.

BMI is not a diagnostic tool for children and adolescents. It is instead used to screen for potential weight and health issues. 
If a child has a high BMI for their age and gender, a health care provider may conduct additional tests to determine if excess fat is a problem. 

Skinfold thickness measurements, family history, dietary and physical activity evaluations and other appropriate health screenings may be included in these assessments.

Centers for Disease Control and Prevention have come up with Body mass index for age percentiles chart separately for boys and girls aged 2 to 20 years. 

After calculating BMI for children and adolescents, it is expressed as a percentile based on a percentile graph. Based on the percentile of a particular child, their weight category is determined.

The following is the table provided by the CDC that categorises BMI for the age of individuals according to their respective percentiles obtained from the percentile chart.

Waist circumference

The waist circumference is used to calculate central obesity. Abdominal obesity is defined by a waist circumference of more than 102 cm in men and more than 88 cm in women.

Waist-to-hip ratio 

The International Diabetes Federation (IDF) has recommended cutoffs for waist circumference and waist-hip ratio. 

The IDF's waist circumference recommendations are not only gender-specific but also population and geography-specific. 
In the Asian population, the waist-hip ratio of 0.80 in women and 0.95 in men signifies abdominal obesity. A ratio less than that is usually considered ideal.

Waist-to-height ratio 

A person's waist-to-height ratio (WHtR) is defined as the waist circumference divided by the height, both in the same units.

According to NICE (The National Institute for Health and Care Excellence), a healthy waist-to-height ratio is 0.4-0.49, which implies no increased health risks. 

A ratio of 0.5-0.59 reveals an increased risk, and high risk is evident from a ratio greater than 0.6.

Factors affecting BMI

Several factors may influence an individual's BMI, which are:

Age: 
Metabolism and body muscle mass change with age, which affects the interpretation of BMI.
Gender: 
Men and women have varying fat distribution patterns, which tend to affect BMI readings.
Lifestyle: 
Sedentary lifestyles or extremely high or low levels of physical activity can greatly influence BMI. If smoking is a part of your lifestyle, it may also cause your BMI to fluctuate. 
Genetics: 
Genetic predispositions can influence metabolism, body composition, and BMI.

The following factors influence an individual's weight and thereby affect their Body Mass Index (BMI).
 

• Improper diet
• Lack of physical activity
• Sedentary lifestyle
• Inadequate sleep
• Alcohol and smoking
• Medication

Importance and Calculation

The simplest way to know whether your weight lies in a healthy range related to your height is by calculating your Body Mass Index (BMI). It generally gives an idea about possible risks for health that could emanate from being underweight, being overweight, or being obese.

This blog will guide you through simple calculations of BMI, why it is important, how to use a BMI calculator and more.  
Read on for an in-depth insight!

BMI is a standardised measure that determines whether an individual's weight is within a healthy range. It is useful for assessing possible health risks that come with being underweight or overweight, such as:

●Cardiovascular diseases
●Type 2 diabetes
●Hypertension
●Sleep apnea
●Certain types of cancer

BMI is not a diagnostic tool but a very important beginning step for further health evaluation.

Understanding BMI Categories

BMI values are grouped into categories to make results easier to interpret. These categories are standardised by the World Health Organization and other health agencies:

Category BMI Range Health Implications
Underweight < 18.5 Risk of malnutrition and other health issues
Normal Weight 18.5 – 24.9 Lower risk of chronic diseases
Overweight 25.0 – 29.9 Increased risk of cardiovascular diseases
Obesity (Class I) 30.0 – 34.9 High risk of metabolic disorders
Obesity (Class II) 35.0 – 39.9 Very high risk of chronic illnesses
Obesity (Class III) ≥ 40.0 Extremely high health risks

Who shouldn't use a BMI calculator? 

BMI is not entirely independent of height. It overestimates obesity in shorter people while underestimates it in taller people. 

As a result, BMI should not be used as a guide for adults who are either shorter than 150 cm or taller than 190 cm.

Risks of being overweight 

Obesity and overweight may increase the risk of certain health problems and emotional and social issues.
 

Health risks of being overweight include
 

• High blood pressure
• Type 2 Diabetes
• Few cancers - Breast cancer
• Fatty liver disease
• Respiratory disease
• Sleep apnea
• Cardiovascular diseases
• Stroke
• Kidney disease
• Osteoarthritis
• Pregnancy problems
• Metabolic syndrome

Using an Online BMI Calculator
An online BMI calculator makes BMI calculation much easier by allowing you to input your Weight and height directly. Most calculators provide results immediately, and some may even include more features, such as: 

●Age-specific BMI calculations
●Gender and activity level adjustments
●Charts and recommendations based on the results

Steps to Use an Online BMI Calculator

1.Visit a reputable website providing a BMI calculator.
2.Enter your Weight and height in the fields as indicated.
3.Click "Calculate" to see your BMI value along with your weight category.
4.Check for any recommendations or information provided. 

Risks of being underweight 

Underweight can be due to genetics, increased metabolism or eating disorders like Anorexia nervosa. Being underweight increases the health risks of a person. These include

• Poor stamina
• Nutritional deficiencies
• Infertility
• Weak Immune System
• Anaemia - especially Iron deficiency anaemia
• Hair Loss
• Amenorrhea and Pregnancy complications in Women
• Osteoporosis

BMI limitations

For adults 

• In athletes and people with a muscular build, BMI is more likely to overestimate the body fat content.
• There is also a chance for overestimating body fat in older people and those who have lost muscle mass.

For children

• Factors such as puberty alter the link between BMI and body fat in adolescents.
• While BMI predicts excess body fat in obese children, elevated BMI levels in overweight children can be caused by an increase in either fat or non-fat mass.

Although BMI is a commonly utilized measure, it has several limitations:

Does Not Measure Body Fat:
The body mass index does not distinguish between fats and muscles. So a muscular person may have a higher BMI with lower body fat.
Does Not Consider Fat Distribution:
Abdominal fat is more dangerous than fat found in other parts of the body. However, BMI does not consider this aspect.
Age and Gender Variations:
BMI does not account for variations in body composition with age and gender.
Ethnic Variations:
Different ethnic groups will have varying risks of diseases with the same BMI.

Ponderal Index 

Ponderal Index (PI) is also called Rohrer's or corpulence index. 

This index integrates an individual's weight and height to produce a value that can classify a person's body weight as normal or abnormal. 

The ponderal index is considered superior to Body Mass Index (BMI). 

This is based on the grounds that BMI considers the body height to be a two-dimensional square. In contrast, the ponderal index considers the body height to be a three-dimensional cube. 

BMI uses the same formula for adults and infants, whereas PI uses a slightly different formula for infants than adults. 

Ponderal Index Formula

For infants

Ponderal index = (Birth weight (g) × 100) ÷ (Crown heel length (cm))3

For adults 

Ponderal index = Weight (Kg) ÷ (Height (m))3

Ponderal Index range

Infants

Adults

How to Maintain a Healthy BMI?

To maintain healthy BMI levels, consider the following tips: 

Adopt a Balanced Diet:
Emphasize the intake of nutrient-rich foods, such as lean proteins, whole grains, fruits, and vegetables.
Stay Active:
Engage your body in regular physical exercises, including cardio, strength training, or yoga.
Monitor Your BMI:
Use BMI calculators regularly to keep track of your body mass index and adjust your fitness and weight management goals accordingly.   
Get Adequate Sleep:
Poor sleep schedules can easily disrupt metabolism, resulting in weight gain.
Actively Deal With Stress:
Chronic stress affects BMI levels, contributing to unhealthy weight fluctuations. Practising relaxation techniques such as deep breathing or meditation on a daily basis may help.

Conclusion

BMI is a valuable indicator for deciding the health of a person. While determining the disease risk, the distribution of fat in the body is more important than the quantity, due to which waist circumference is thought to be a better predictor of a health risk than BMI. 

Otherwise, BMI is reliable to an extent and is an easy way to predict an individual's overall health. We also have the ponderal index to measure the body composition of a person, which is considered more accurate than BMI.

A simple BMI calculation gives an individual insight into the weight category to which they currently belong. A good BMI calculator helps one assess their BMI level and understand the outcome while taking active steps towards healthy weight maintenance. 

Even though BMI does not completely indicate an individual’s health status, it remains an excellent starting point for discussions with healthcare professionals. A well-balanced lifestyle and frequent monitoring will enable one to keep one's BMI at optimal levels.