What FRAX does

FRAX is a calculator that estimates your probability of breaking a bone in the next ten years. It gives two numbers: the risk of a major osteoporotic fracture (spine, hip, forearm or upper arm) and, separately, the risk of a hip fracture.

Its purpose is to move the conversation past a single density number. Two women can have identical bone density and quite different fracture risk, because age, weight, previous fractures and other factors carry independent weight.

What it asks and why

  • Age and sex — risk rises steeply with age independently of density.
  • Weight and height — low body weight raises risk.
  • Previous fracture as an adult — one of the strongest single predictors. A fracture from a fall at standing height counts.
  • Parent with a hip fracture — family history carries independent weight.
  • Current smoking and alcohol of three or more units a day.
  • Glucocorticoids — current or past prolonged oral steroid use.
  • Rheumatoid arthritis and secondary osteoporosis causes.
  • Femoral neck bone density — optional. FRAX works without it, and works better with it.

How the numbers are used

In the United States, the Bone Health and Osteoporosis Foundation has long framed treatment thresholds for postmenopausal women with low bone mass at a 10-year probability of 3% or more for hip fracture or 20% or more for major osteoporotic fracture. These are decision aids for a conversation, not automatic instructions.

Four limitations worth knowing before you trust the number

  1. It does not ask about falls. Falls history is one of the strongest predictors of actually breaking a bone, and FRAX does not capture it. A woman who falls repeatedly can have a reassuring FRAX score and a genuinely high risk.
  2. Risk factors are yes or no, not dose or duration. Two years of high-dose steroids and three months of low-dose count the same.
  3. It does not use spine density. Only femoral neck density is entered, so a woman whose spine is much worse than her hip can be underestimated.
  4. It does not include the reason for early menopause. Premature ovarian insufficiency and surgical menopause mean far more years of low estrogen, and the tool does not account for that directly.

How to use it sensibly

Run it before your appointment, write down both numbers, and bring the questions the numbers raise rather than the numbers alone. If your result sits near a threshold, that is precisely the situation where the factors FRAX cannot see — falls, spine density, how early your menopause was — should decide the direction.

A worked example

Two women, both 62, both with a T-score of −2.2 at the femoral neck.

The first weighs 70 kg, has never fractured, does not smoke, and has no family history. The second weighs 52 kg, broke her wrist at 58 in a fall from standing, and her mother fractured a hip. Same density, materially different ten-year probability — and in most versions of this comparison, only the second crosses a treatment threshold.

That gap is the entire point of the tool. A density number alone would have treated these two women identically.

Where to run it

FRAX is free and hosted by the University of Sheffield, with country-specific versions because fracture rates differ between populations. Use the version for the country you live in — running the wrong country's model produces a number that does not mean what you think it does.

What to do with a borderline result

If your result sits just under a threshold, that is the situation where the tool's blind spots decide the direction. Raise these explicitly:

  • Have you fallen in the last year? FRAX does not ask, and it is one of the strongest predictors of actually breaking a bone.
  • What is your spine density? FRAX uses only femoral neck. A spine much worse than the hip changes the picture.
  • How old were you at menopause? Early or surgical menopause means more years of low estrogen than the model accounts for.
  • Have you lost height? Height loss can indicate a vertebral fracture that was never diagnosed — and a prior vertebral fracture changes the calculation entirely.

What FRAX is not

It is not a diagnosis, and it does not replace bone density testing. It is a risk estimate designed to help decide whether treatment is worth starting. A low score in a woman who falls frequently, or who has already fractured a vertebra without knowing it, is a false reassurance rather than a clean bill of health.