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Free Online BMI & Age Calculator

Welcome to the most accurate BMI and Age Calculator online! Our user-friendly tool helps you:

Perfect for fitness enthusiasts, healthcare professionals, and anyone monitoring their health journey.

BMI Calculator

Under
Normal
Over
Obese

Underweight: <18.5

Normal: 18.5–24.9

Overweight: 25–29.9

Obese: ≥30

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Age Calculator

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Tools & Options

BMI History

    BMI Information

    BMI Introduction

    BMI is a measurement of a person's leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height. Specifically, the value obtained from the calculation of BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese depending on what range the value falls between. These ranges of BMI vary based on factors such as region and age, and are sometimes further divided into subcategories such as severely underweight or very severely obese. Being overweight or underweight can have significant health effects, so while BMI is an imperfect measure of healthy body weight, it is a useful indicator of whether any additional testing or action is required. Refer to the categories shown in the results or the visual scale to see the different ranges used by the calculator.

    Limitations of BMI

    Although BMI is a widely used and useful indicator of healthy body weight, it does have its limitations. BMI is only an estimate that cannot take body composition into account. Due to a wide variety of body types as well as distribution of muscle, bone mass, and fat, BMI should be considered along with other measurements rather than being used as the sole method for determining a person's healthy body weight.

    In adults:

    BMI cannot be fully accurate because it is a measure of excess body weight, rather than excess body fat. BMI is further influenced by factors such as age, sex, ethnicity, muscle mass, body fat, and activity level, among others. For example, an older person who is considered a healthy weight, but is completely inactive in their daily life may have significant amounts of excess body fat even though they are not heavy. This would be considered unhealthy, while a younger person with higher muscle composition of the same BMI would be considered healthy. In athletes, particularly bodybuilders who would be considered overweight due to muscle being heavier than fat, it is entirely possible that they are actually at a healthy weight for their body composition. Generally, according to the CDC:

    In children and adolescents:

    The same factors that limit the efficacy of BMI for adults can also apply to children and adolescents. Additionally, height and level of sexual maturation can influence BMI and body fat among children. BMI is a better indicator of excess body fat for obese children than it is for overweight children, whose BMI could be a result of increased levels of either fat or fat-free mass (all body components except for fat, which includes water, organs, muscle, etc.). In thin children, the difference in BMI can also be due to fat-free mass.

    That being said, BMI is fairly indicative of body fat for 90-95% of the population, and can effectively be used along with other measures to help determine an individual's healthy body weight.

    Risks associated with being overweight

    Being overweight increases the risk of a number of serious diseases and health conditions. Below is a list of said risks, according to the Centers for Disease Control and Prevention (CDC):

    As can be seen from the list above, there are numerous negative outcomes that may result from being overweight. Generally, a person should try to maintain a BMI below 25 kg/m², but ideally should consult their doctor to determine whether or not they need to make any changes to their lifestyle in order to be healthier.

    Risks associated with being underweight

    Being underweight has its own associated risks, listed below:

    In some cases, being underweight can be a sign of an underlying condition like anorexia nervosa. Consult your doctor if you think you or someone you know is underweight, particularly if the reason isn't obvious.

    BMI formula

    Below are the equations used for calculating BMI in the International System of Units (SI) and the US customary system (USC), using a 5'10", 160-pound individual as an example:

    USC Units:

    BMI = 703 × (mass (lbs) / height² (in))

Example (5'10", 160 lbs):
Height = 5 feet * 12 inches/foot + 10 inches = 70 inches
BMI = 703 × (160 lbs / (70 in)² )
BMI = 703 × (160 / 4900)
BMI = 703 × 0.03265...
BMI ≈ 23.0

    SI, Metric Units:

    BMI = mass (kg) / height² (m)

Example (5'10", 160 lbs):
Height = 70 inches = 70 * 0.0254 m = 1.778 m
Weight = 160 lbs = 160 * 0.453592 kg ≈ 72.57 kg

BMI = 72.57 kg / (1.778 m)²
BMI = 72.57 / 3.161284
BMI ≈ 23.0

    Frequently Asked Questions (FAQ)

    BMI Calculator

    What is BMI?

    BMI (Body Mass Index) is a numerical value calculated from your weight and height that provides a reliable indicator of body fatness for most people.

    How accurate is BMI?

    While BMI is a useful screening tool, it doesn't directly measure body fat. Athletes with high muscle mass may have a high BMI without excess fat. Age, sex, ethnicity, and muscle mass influence its accuracy. See the 'Limitations of BMI' section above for more details.

    What are the BMI categories?
    • Underweight: <18.5
    • Normal weight: 18.5 – 24.9
    • Overweight: 25 – 29.9
    • Obese: ≥ 30

    This calculator also provides tailored health tips for each category.

    Should children use this calculator?

    Our tool uses the standard adult formula. Children and adolescents' BMI requires interpretation using age and sex-specific percentile charts due to their growth patterns. Consult a healthcare provider for children's BMI assessment.

    Is the uploaded image stored anywhere?

    No. The image you select is only displayed locally in your browser for the current session using JavaScript's FileReader API. It is not uploaded or stored on our servers. Refreshing the page will clear the image.

    Age Calculator

    How does the age calculator work?

    It precisely calculates the time elapsed between your specified date of birth and either today's date or another specific date you enter in the 'Calculate Age At' field.

    Can I calculate age at a future date?

    Yes! Simply enter your date of birth and then select the desired future date in the 'Calculate Age At' field. The calculator will show how old you will be on that specific day.

    Why does the calculator show months and days?

    Displaying age in years, months, and days offers a much more precise measure than just years alone. This detail can be important for various reasons, including tracking developmental milestones in children, eligibility for certain events or benefits, or simply for personal interest.