BMI — Where Your Weight Should Be


A super-quick review for those of you who snuck into this article form the back door: we dFolk are bombarded with numbers, goals, and targets. We're frequently told where we should be, but not how high our risk is when we can't reach our targets. In this series of discussions we look at all of our important numbers and break them down into a simple green light, yellow light, red light format to put all of your critical numbers into a useful context. To give you perspective on when and how much to worry. When to relax, when to call your doc, and when to call 911.

Discussing BMI is a weighty matter (OK, I won't be quitting my day job anytime soon). BMI looks at your height and your weight to determine if you are at a healthy weight, a bit plump, or scale-crushingly overweight. It's not a perfect system. It can't allow for frame — whether you're big boned or delicate. It's frequently pointed out that body builders have BMIs that would suggest they are fat, but that's true only because muscle is heavier than fat. If you have lots, and lots, and lots of super-big muscles you'll weigh more than a typical person of your height, and that throws off your BMI score. Of course, this is usually pointed out by people who don't want to face up to their BMI scores. And of course, we use a whole different system for growing children.

But, despite imperfections, BMI tells you in rough terms how you compare to a "healthy" population, and it also lets you track changes in your weight-health over time. Check out your BMI on this handy calculator.

Green light BMI score

The official goal for your Body Mass Index is under 25. Therefore, the green light range for your BMI score is 18.5 to 24.9.


Yellow light BMI score

We tend to worry about BMI being too high, but it can be too low as well. So the BMI yellow light comes in both high and low flavors. The high yellow light is between 25.0 and 29.9; the higher you are, the greater your risk. You might want to think twice about that second plate of spaghetti if your BMI is 28.7; but if you are at 25.1 you might have better things to fret about. The low BMI yellow light is any score under 18.5, which is considered underweight — also unhealthy. While it might seem adding weight would be significantly easier (and more fun) than losing weight, don't be jealous. Most folks with shockingly low BMIs have difficult metabolic issues or eating disorders.

Red light BMI score

The red light scores for BMI start at 30.0, and are rudely classified as "obesity." The more obese you are, the greater the health threats you face. The deeper into the red you go, the more dangerous it is. There are several different medical classifications of obesity, but above 40 is classified as "extreme obesity." For reference, the average height of a woman in the U.S. is 5 foot, 4 inches tall, according to Centers for Disease Control statistics. To clock in with a BMI of 40, our average woman would need to tip the scales at 233 pounds, about 80 pounds more than a healthy woman of the same height. Picture yourself walking around wearing an 80 pound coat all day long. But it can get worse than that. I've seen patients with BMIs in the 50s, and at that point you're twice the person you should be. Literally.

Logically, there must be a low BMI red light, but I couldn't find any data on how much underweight you need to be before you're staring a life-threatening situation in the face.

Related to BMI is the subject of waist circumference. If your waist is more than 40 inches and you're a man, or more than 35 inches if you're a woman, it's considered "abdominal obesity," and is a significant risk factor for metabolic syndrome, the chain of events that can lead to type 2 diabetes.


The BMI green light is between 18.5 and 24.9.

The BMI yellow light is between 25.0 and 29.9 on the high end, and below 18.5 on the low end.

The BMI red light is greater than 40.


Read Diabetes by the Numbers in full.

Last Modified Date: November 28, 2012

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