Fracture Risk Calculator (OST Score): Estimate Your Osteoporosis Risk

What Is the OST (Osteoporosis Self-Assessment Tool)?

The Osteoporosis Self-Assessment Tool, commonly abbreviated OST, is a simple screening calculation that uses only two numbers — your body weight and your age — to flag whether you might be at higher risk of low bone density and osteoporosis. It was developed as a fast, no-cost way to help identify people, particularly postmenopausal women, who are more likely to benefit from a formal bone density scan (DXA), before more detailed clinical risk tools or imaging are used.

OST is deliberately minimalist. Unlike more detailed fracture risk models that ask about smoking, alcohol use, prior fractures, family history, and steroid use, OST relies on the simple, well-documented relationship between lower body weight, older age, and lower bone mineral density. The tradeoff is that OST is meant purely as an initial screening flag — not a diagnosis, and not a substitute for a full clinical fracture risk assessment.

How This Calculator Works

The formula’s logic is straightforward once you see it: being heavier tends to be protective for bone density (more skeletal loading and more peripheral estrogen production in fat tissue, particularly relevant after menopause), while being older tends to be a risk factor, since bone density naturally declines with age. Subtracting age from weight (in kg) and scaling by 0.2 produces a score where higher, less-negative numbers indicate lower risk, and more deeply negative numbers indicate higher risk.

This calculator uses the same formula and the same three-tier risk cutoffs described in peer-reviewed literature evaluating OST’s screening performance, so the number you get here should match what you’d calculate by hand from your own weight and age.

Understanding Your OST Risk Category

These cutoffs come from published validation studies of the OST tool and are widely cited in clinical reviews of osteoporosis screening instruments. A “moderate” or “high” result is a signal to discuss bone density testing with your doctor — it is not itself a diagnosis of osteoporosis or low bone mass.

Why Weight and Age Are the Only Two Factors

It might seem surprising that a bone health screening tool ignores so many factors that clinicians normally care about — diet, exercise, smoking, alcohol, family history, medication use. The reason OST works reasonably well despite this simplicity is that weight and age are two of the single strongest, most consistently reproduced predictors of bone mineral density across large population studies. Adding more inputs to a screening tool can improve accuracy somewhat, but it also makes the tool harder to use quickly, which defeats the purpose of a fast first-pass screen.

Research validating OST across multiple ethnic populations and age groups has found it performs comparably to more complex multi-factor tools for the specific job of flagging who should get a DXA scan, even though it captures far less information about each individual. That’s the whole point of a screening tool: it doesn’t need to be perfectly accurate for every person, it needs to be good enough, fast enough, and simple enough that more people actually use it.

What OST Doesn’t Tell You

Because OST is intentionally simple, it has real limitations worth understanding before you rely on your result:

It doesn’t diagnose osteoporosis. Only a DXA (dual-energy X-ray absorptiometry) bone density scan, interpreted by a clinician, can do that. OST simply estimates the likelihood that a scan would find low bone density.

It ignores major independent risk factors. A prior fragility fracture, long-term corticosteroid use, a parental history of hip fracture, smoking, heavy alcohol use, rheumatoid arthritis, and early menopause are all independently linked to fracture risk regardless of what your OST score says.

It was primarily validated in postmenopausal women. Most of the research behind OST focused on women past menopause, since that’s the population with the sharpest rise in osteoporosis risk. It’s sometimes applied more broadly, but its accuracy in men and in younger women is less well established.

Being high-weight isn’t automatically protective. While higher body weight is statistically associated with somewhat higher bone density on average, this doesn’t mean weight gain is a recommended strategy for bone health, and other health risks associated with excess weight aren’t reflected in this score at all.

Who Should Get a DXA Bone Density Scan

General screening guidance (which your own doctor may adjust based on your specific history) typically points toward DXA testing for:

Women age 65 and older, regardless of additional risk factors, since fracture risk rises substantially in this group.

Postmenopausal women under 65 who have at least one additional risk factor, such as low body weight, a parental history of hip fracture, or prior fracture as an adult.

Men age 70 and older, or younger men with significant risk factors such as long-term steroid use or a history of low-trauma fracture.

Anyone, of any age, who has broken a bone from a fall from standing height or less — a “fragility fracture” — since this itself is one of the strongest predictors of future fracture risk and usually warrants imaging regardless of a screening score.

An OST result in the moderate or high risk range is a reasonable prompt to raise DXA testing with your doctor if you haven’t already had one, particularly if it lines up with other risk factors you’re aware of.

Other Fracture Risk Factors Worth Discussing With Your Doctor

If your OST score comes back in a concerning range, or even if it doesn’t but you have other risk factors, it’s worth discussing the following with a clinician, since none of them are captured by this calculator:

Fracture history. A previous fracture from a minor fall roughly doubles the risk of a future fracture.

Family history. A parent who fractured a hip is an independent risk factor, separate from your own bone density.

Medications. Long-term oral corticosteroid use (such as prednisone) is one of the strongest medication-related risk factors for bone loss.

Lifestyle factors. Smoking, heavy alcohol intake, and low physical activity are all independently associated with lower bone density.

Hormonal factors. Early menopause (before age 45), or conditions and treatments that lower estrogen or testosterone, accelerate bone loss.

Other medical conditions. Rheumatoid arthritis, celiac disease, hyperthyroidism, and chronic kidney disease are all linked to increased fracture risk.

Many clinicians combine a bone density result with a validated multi-factor tool (such as FRAX, a proprietary algorithm not used in this calculator) to estimate an actual 10-year probability of major fracture, which factors in several of the items above alongside bone density.

How Fracture Risk Changes With Age and Menopause

Bone is living tissue that is constantly being broken down and rebuilt throughout life, in a process called remodeling. Through early adulthood, bone formation generally keeps pace with breakdown, and bone mass typically peaks somewhere in the late twenties to early thirties. After that, bone breakdown gradually starts to outpace formation for most people.

For women, this gradual decline speeds up dramatically around menopause, when falling estrogen levels remove a hormone that had been helping to restrain bone breakdown. Women can lose a meaningful percentage of bone density in the five to seven years immediately surrounding menopause, which is a major reason osteoporosis screening guidelines focus heavily on postmenopausal women. Men experience a more gradual, later decline in bone density, generally tied to slowly falling testosterone levels with age, which is part of why male-specific screening thresholds tend to start at an older age.

What To Do If You’re in the Moderate or High Risk Category

A moderate or high OST result is not a cause for panic, but it is worth acting on. Reasonable next steps generally include:

Ask your doctor about a DXA scan if you haven’t had one, especially if your score is combined with other risk factors described above.

Review your calcium and vitamin D intake, since both are foundational nutrients for bone health, and many adults don’t get enough of one or both through diet alone.

Incorporate weight-bearing and resistance exercise, which is one of the few interventions consistently shown to help maintain or modestly improve bone density and, just as importantly, improve balance and reduce fall risk.

Have a fall-risk conversation, particularly if you’re older or have balance issues, since most fragility fractures result from a fall, not from bone weakness alone.

Ask about medication options if a DXA scan confirms osteoporosis or osteopenia, since several well-studied prescription treatments can meaningfully reduce fracture risk in people who are diagnosed.

Frequently Asked Questions

Is a negative OST score always bad?
Not necessarily. Most people, especially older adults, will have a negative OST score, since age is subtracted from weight in the formula. What matters is which risk band the number falls into, not whether it’s negative in an absolute sense.

Can I use this if I’m a man?
Yes, you can calculate the score, but keep in mind most of the validation research behind OST focused on postmenopausal women. Male-specific bone density screening guidelines and thresholds may differ from what’s shown here.

How is OST different from FRAX?
FRAX is a more detailed, proprietary fracture risk algorithm that incorporates around a dozen factors, including bone density (if available), fracture history, smoking, alcohol use, and steroid use, to estimate a 10-year fracture probability. OST is a much simpler two-factor screening tool meant to flag who might benefit from further testing like a DXA scan or a FRAX assessment; this calculator uses only the open OST formula, not the FRAX algorithm.

Does gaining weight lower my fracture risk?
Statistically, higher body weight is associated with somewhat higher bone density, but this calculator isn’t a reason to pursue weight gain as a health strategy. Weight-bearing exercise, adequate calcium and vitamin D, and avoiding smoking and excess alcohol are the interventions actually recommended for bone health.

My score is “low risk” — does that mean I definitely don’t have osteoporosis?
No. A low-risk OST score reduces the statistical likelihood of a low DXA result but doesn’t rule it out, and doesn’t account for fracture risk factors unrelated to bone density, like a fall-prone environment or a medication that affects balance. If you have symptoms or specific concerns, discuss them with your doctor regardless of your score.