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BMI – What It Is & How It Changes Your Insurance

BMI; that tool that nobody likes but everyone uses. “What is a Body Mass Index anyway and why should I care?”. And more importantly for us in this forum, what does it have to do with personal insurance?

Key Points:

  • BMI – What is it?
  • How is it used for insurance?
  • What are the downsides to this measurement?


Body Mass Index is a simple tool that quickly informs people about potential physical characteristics. What do we mean by that? Do I mean being over-weight or under-weight? Partly, but there is also more to it than that. Before we answer those questions, let’s back up a bit and dissect what the measurement actually is.

The calculation for BMI = mass / height^2, specifically Kg/m^2. Or put simply, if you weigh 60Kg are you are 1.8m tall, then your BMI is 18.5. Use this calculator to find out your own BMI. The index is a ratio of your height (squared) to weight.

The World Health Organisation (WHO) characterises BMI in the following table. You will notice in the example I just used that an index of 18.5 would mean the person was just in the ‘normal’ range, bordering on ‘Mild Thinness’.

CategoryBMI Range
Severe Thinness< 16
Moderate Thinness16 – 17
Mild Thinness17 – 18.5
Normal18.5 – 25
Overweight25 – 30

Obese Class I

Obese Class II

30 – 35

35 – 40

Obese Class III> 40

How is it used in insurance?

When you apply for personal insurance (such as life cover, income protection or private health & medical), two key questions will be asked; your height and weight. Insurance companies want to know the type of ‘risk’ that you pose to them. How healthy are you, really? A high BMI or a low BMI can indicate several pre-existing conditions or future issues that may present. Both are therefore potential risks.

A high BMI can be an indicator of:

  • High blood pressure
  • Higher levels of LDL cholesterol, which is widely considered “bad cholesterol”
  • Type II diabetes
  • Coronary heart disease
  • Stroke

 A low BMI can be an indicator of:

  • Malnutrition, vitamin deficiencies, anaemia
  • Osteoporosis
  • A decrease in immune function

There are other risk factors which may also be present, this list is not exhaustive.

As I’ve discussed here before, there are only four things that the insurance company can do with your application. These possible outcomes are:

      1. Your application is accepted as standard
      2. Or you are denied cover (possibly as a deferral for 12 months).
      3. Or, you receive a policy with standard pricing, covering all conditions, but with an exclusion on the specific condition you mentioned in your application – in this case, having a high/ low BMI (and, sometimes, related conditions as per the above).
      4. You get cover, but your premium is increased to offset the “risk” you pose to the insurer.

What are the downsides to this measurement?

The Body Mass Index is not a perfect tool. Some people are perfectly healthy but are naturally of a certain body composition that would make them appear to be “obese” or “severely thin”, according to WHO’s definition.

Sports people often fall foul of this measure, especially if they have developed higher than ‘normal’ muscle mass. Muscle being denser than fat, skews the index disproportionally.

Insurance companies, and the underwriters who determine your ‘risk’, usually work hard to find out the relevant information that is specific to your situation. If you do not present any other health triggers or factors, then there is a good chance (depending on the level of the index), that you can get your standard cover at standard rates. The index allows the underwriters to quickly ask questions about the state of your health, while they gather further medical information.

As with all things in personal insurance, it pays not to make assumptions about your cover. One thing that is often overlooked, is that if your weight changes, and your BMI changes, this might be a positive step that the insurance company will view favourably (possibly enough to even reduce your premium). The best thing you can do is ask your professional financial adviser. They will guide you to your next steps.

Check out the other calculators we have here.