What this BMI guide covers
What BMI should I be?
Most adults fall into a healthy range between 18.5 and 24.9, but that number is not always a true reflection of your health. Things like muscle mass, body shape, gender and ethnicity can all influence what is actually healthy for you.
Is BMI inaccurate?
BMI gives a general sense of risk, but it does not measure body fat, muscle, or fat distribution. We will look at where it can be useful and where it often falls short.
Are there better ways to track your health and weight loss progress?
Yes. This blog explores a number of other methods that are often more reliable and relevant to your individual body.
If you have ever looked up your BMI and felt confused or discouraged, you are not alone. This blog explains what BMI really means, where it came from, what I use as a weight loss coach, and how to use it alongside other tools to make smarter decisions about your health and fitness goals. Read on:
What Is BMI and Where Did It Come From
BMI stands for Body Mass Index. It is a simple calculation that uses your weight and height:
BMI = weight in kilograms divided by height in metres squared
The formula was created in the 1830s by Belgian mathematician Adolphe Quetelet. He was trying to describe average human size for population studies. It was never meant to measure individual health. Despite this, it became widely used in public health from the 1970s onwards.
It is still used today because it is simple and quick. However, BMI does not tell you anything about body fat, fitness or how your weight is distributed. That is where it becomes much less helpful on a personal level.
What BMI Should I Be
Here are the common BMI categories used by the NHS and other health services:
Below 18.5 – Underweight
18.5 to 24.9 – Healthy weight
25.0 to 29.9 – Overweight
30.0 to 34.9 – Obese Class 1
35.0 to 39.9 – Obese Class 2
40 and above – Obese Class 3
These ranges are only rough guidelines. A BMI of 26 might be perfectly healthy for someone with lots of muscle. On the other hand, someone with a BMI of 22 might still be at risk if they have low muscle mass and high levels of internal fat.
BMI can give you a ballpark idea of whether your weight might be linked to health risks though, so it is still a useful tool, but it should not be the only measure you rely on.
How BMI Differs by Gender and Ethnicity
BMI applies the same formula to everyone. That means it ignores important differences like gender, age and ethnicity.
Gender Differences
Men and women store fat differently. Women naturally have more body fat than men, even when healthy. Men often carry more fat around the stomach, while women store more around the hips and thighs. BMI does not account for these differences, so it may not reflect your true health status.
Ethnic Differences
People from different ethnic backgrounds may have higher or lower health risks at the same BMI.
- South Asian adults may face increased risk of type 2 diabetes and heart disease at lower BMI levels, sometimes starting at 23
- Black adults often have more lean muscle mass, so a BMI of 27 or 28 may be healthy for them
- East Asian populations may also face higher health risks at lower BMI levels
Although the NHS has acknowledged some of these variations, the standard BMI chart does not take them into account.
When BMI Might Not Be Accurate: Flaws of BMI
BMI has some value as a tool, but it has several important flaws when used on its own.
It does not measure body fat
BMI compares weight and height, not fat and muscle. A muscular person may have a high BMI even if they have very low body fat.
It does not show where fat is stored
Visceral fat around the stomach is more harmful than fat stored in other areas. BMI cannot tell you where your body stores fat.
It ignores individual differences
BMI does not adjust for age, sex, or ethnic background. This leads to inaccurate results for many people.
It can mislabel healthy people
People who are fit and muscular might be told they are overweight or obese, even when their health markers are excellent.
It can offer false reassurance
Someone with a normal BMI could still have unhealthy habits or high levels of internal fat. A healthy BMI does not always mean low risk.
Other Ways to Measure Health
If you want a clearer picture of your health or progress, here are some other tools that can be used alongside BMI.
Waist measurement
This is one of the most useful and accessible ways to track abdominal fat. High waist size is strongly linked to heart disease, diabetes and other conditions.
- Women should aim for a waist under 80cm
- Men should aim for a waist under 94cm
Waist to height ratio
Your waist should be less than half your height. This is a simple, effective way to assess your health risk. For example, if you are 170cm tall, your waist should be under 85cm.
Body composition scans
InBody or DEXA scans break down fat, muscle, and bone. These are more detailed and accurate than BMI, but they are not always available or affordable.
Physical function and how you feel
Health is about more than numbers. Can you walk up a hill without getting out of breath? Do you feel strong, energised and mobile? These indicators are just as important as any calculator.
Why BMI Still Gets Used
BMI is still used by doctors and health systems because it is:
- Easy to calculate with no equipment
- Useful for identifying broad trends in large groups
- A common starting point in screening for weight-related conditions
For individual health, though, BMI is only one part of the picture. It should be used alongside other methods to make decisions that are more personal and relevant.
How I Use BMI with My Weight Loss Clients
When I start working with a new weight loss client, I look at a few different figures to help us understand where they are right now. One of those is their BMI. I do not use it to label anyone or judge progress in isolation. I use it purely as a benchmark, a way to track how things change over time.
Alongside BMI, I also look at weight (including trends overtime), how someone feels in themselves and, with some clients, waist measurements. Not everyone finds those useful, so we only use them when it makes sense.
I might also work out body fat percentage using a calculator, or a bioimpedance scale. Some clients choose to use progress photos for their own reference, which can be a helpful visual guide. I do not ask clients to send me photos, though. I believe that should stay private.
So in short, I use a range of tools. I never rely on just one. Like any good toolbox, it is about choosing the right tool at the right time for the right person. BMI can be part of that, but it is never the full story.
So, What BMI Should You Aim For
The healthy range is officially between 18.5 and 24.9. But this should not be taken as a rule for everyone. If you are active, have a healthy waist size, feel strong, and your habits are improving, your BMI may not be a concern.
Instead of chasing a number, also focus on what you can control. Build routines that support better energy, sleep, mood, and strength. When you do that, weight and health will usually improve as a result.
Looking for a Smarter Approach to Weight Loss
If you are tired of confusing targets, mixed messages, and weight charts that do not reflect your real progress, I can help.
My coaching is built around real habits, not strict rules or fixed numbers. I help people create a lifestyle they can actually stick to, while still making clear and steady progress. If that sounds like what you need, take a look at my personalised weight loss support that fits your body and life.
👉 Find out how to lose weight without obsessing over BMI
👉 Discover smarter ways to track fat loss that work for real life
