Healthy BMI for women by age

Adults: one range for every age

Search for "healthy BMI by age" and you'll find tables suggesting a 50-year-old woman should sit higher than a 25-year-old. For adults, that isn't how UK guidance works. At 22 or at 62, the NHS categories are identical.

The reason is fairly simple. The cut-offs are based on where health risks start to climb, and the risk of type 2 diabetes, heart disease and several cancers begins rising above a BMI of 25 across the whole adult population, not only after a certain birthday.

So where do the age-adjusted tables come from? Usually from average weights rather than healthy ones. Average weight in the UK does tend to creep up through our 30s, 40s and 50s. But "what most people weigh at 50" and "what's healthiest at 50" are different questions, and the charts often blur them together.

Girls under 18

A BMI of 22 means something quite different at 11 than it does at 16, because girls' bodies change so much while they're growing. So for anyone aged 2 to 18, BMI is plotted on a centile chart against other girls of exactly the same age.

A girl on the 50th centile is right in the middle for her age. In UK clinical practice, a child at or above the 91st centile is generally considered overweight and at or above the 98th very overweight, while at or below the 2nd centile is considered underweight. The NHS has a separate calculator for children and teenagers that does this for you.

It's also the reason our calculator isn't meant for anyone under 18. The adult formula simply gives the wrong answer for a growing body.

Women over 65

Official guidance doesn't change at 65, but the research gets more interesting. A large 2014 review of studies in older adults, published in the American Journal of Clinical Nutrition, found the lowest risk of death among people with a BMI of about 27 to 28. That's above the standard healthy band. The same review found risk rose noticeably once BMI dropped below about 23.

Nobody's entirely sure why, but a couple of explanations make sense. A little reserve helps when you're unwell or recovering from an operation. And in later life, a low BMI often goes hand in hand with losing muscle, which affects strength and balance.

None of this means you should try to put weight on after 65. It does mean two practical things: weight loss you haven't planned for is worth mentioning to your GP, and a BMI of 26 at 72 isn't the same worry it might be at 32. It's one of the reasons our calculator isn't designed for over-65s either.

What really does change as you get older

The range stays put, but your body doesn't. Three changes are worth knowing about because they affect what your BMI is actually telling you.

You gradually lose muscle

From around your 30s, muscle slowly declines unless you do something to keep it. Two women with the same BMI, one at 25 and one at 60, can have very different amounts of muscle and fat. BMI can't see that difference at all, which is one of the reasons BMI isn't always accurate for women.

Fat moves to the middle

Around and after the menopause, falling oestrogen means more fat tends to settle round your tummy rather than your hips and thighs. That's why a waist measurement becomes especially useful from your mid-40s. Our guide to BMI and menopause goes into this in more detail.

You may get a little shorter

Many people lose a centimetre or two in height over the decades. Same weight, less height, and your BMI edges upwards without anything else changing. If you haven't been measured in years, it's worth doing again.

A decade-by-decade view

The healthy range is the same in every row. What changes is what's worth paying attention to.