FRAX® Score Calculator
Estimates 10-year probability of major osteoporotic fracture and hip fracture using clinical risk factors with or without femoral neck BMD. Developed by the University of Sheffield — the reference standard for fracture risk assessment in adults aged 40–90.
Estimate FRAX® Fracture Risk
Enter the patient’s demographics, anthropometrics, and clinical risk factors below. Femoral neck BMD T-score is optional — the tool provides estimates with or without it. BMI is auto-calculated from height and weight.
This calculator uses a simplified model based on published relative risks from FRAX® validation studies. It provides an educational estimate only. For clinical decision-making, use the official FRAX® tool at frax.shef.ac.uk, which incorporates country-specific fracture and mortality data with the full validated algorithm.
Understanding FRAX®
FRAX® (Fracture Risk Assessment Tool) was developed by the WHO Collaborating Centre for Metabolic Bone Diseases at the University of Sheffield, led by Professor John Kanis. First released in 2008, it uses clinical risk factors — with or without femoral neck BMD — to estimate the 10-year probability of a major osteoporotic fracture (hip, clinical spine, forearm, or proximal humerus) and of hip fracture specifically.
The algorithm integrates hazard ratios from multiple large population-based cohorts (over 60,000 patients, 250,000 person-years of follow-up) with country-specific fracture incidence and mortality data. FRAX® models are currently available for 73 countries, making it the most widely used fracture risk assessment tool globally.
Two Output Probabilities
1. Major Osteoporotic Fracture: 10-year probability of fracture at hip, clinical spine, forearm, or proximal humerus — the four sites with the greatest clinical and economic impact.
2. Hip Fracture: 10-year probability of hip fracture specifically — the most devastating osteoporotic fracture, associated with 20–30% one-year mortality in the elderly.
With vs Without BMD
FRAX® can be calculated without BMD using clinical risk factors alone — this is useful in primary care for initial screening and for deciding who needs a DXA scan. When femoral neck BMD T-score is entered, the estimate becomes more precise. FRAX® is validated only for femoral neck BMD, not lumbar spine, total hip, or other DXA sites.
Importantly, a normal BMD does not eliminate fracture risk if clinical risk factors are present. FRAX® captures risk beyond BMD alone.
Key concept: FRAX® estimates fracture probability — not bone density. Two patients with identical T-scores may have very different FRAX® results based on age, prior fracture history, and other clinical factors. Treatment decisions should be based on fracture probability, not BMD alone.
Interpretation & Treatment Thresholds
Treatment thresholds vary by country and guideline body. The most widely referenced are the UK NOGG (National Osteoporosis Guideline Group) and US NOF (National Osteoporosis Foundation) thresholds. Always apply local guidelines.
| Guideline | Treat If Major Fracture Risk | Treat If Hip Fracture Risk | Notes |
|---|---|---|---|
| US — NOF/AACE | ≥ 20% | ≥ 3% | Fixed thresholds; widely used for treatment initiation |
| UK — NOGG | Age-dependent thresholds | Compares to fracture probability of a woman with a prior fracture at the same age | |
| Canada — Osteoporosis Canada | ≥ 20% | — | Major fracture threshold primary; 10–20% = moderate risk → shared decision |
Practical Three-Zone Approach (US/NOF)
The US NOF hip fracture threshold of ≥ 3% was derived from a cost-effectiveness analysis specific to the US healthcare system. This threshold may not be appropriate in other countries with different healthcare costs and fracture epidemiology. Always use country-specific FRAX® models and local guideline thresholds for clinical decisions.
Clinical Details & Risk Factor Guidance
Each FRAX® clinical risk factor has specific definitions and clinical nuances that affect correct scoring. Misclassification of risk factors is one of the most common sources of error when using the tool.
This refers to a fragility fracture occurring in adult life spontaneously or from a force equivalent to a fall from standing height or less. It is the single strongest clinical risk factor for future fracture — a prior fracture approximately doubles the risk of a subsequent fracture.
- Include: Vertebral fractures (clinical or morphometric), hip, wrist/forearm, proximal humerus, rib, pelvic fractures occurring from minimal trauma.
- Exclude: High-energy fractures (road traffic accidents, sports injuries), skull fractures, pathological fractures due to local malignancy, and fractures of the fingers, toes, and face.
- Morphometric vertebral fractures (found incidentally on imaging) count as previous fractures in FRAX®, even if they were asymptomatic.
FRAX® does not differentiate by the number, site, or recency of prior fractures — each of these factors independently increases risk beyond what the single yes/no input captures. A patient with multiple recent vertebral fractures is at substantially higher risk than the FRAX® estimate suggests.
FRAX® defines glucocorticoid exposure as current or previous use of oral glucocorticoids for ≥ 3 months at a dose of ≥ 5 mg prednisolone daily (or equivalent). This is a binary yes/no input — the standard FRAX® model does not differentiate between moderate and high-dose glucocorticoids.
However, the risk is strongly dose-dependent in reality:
- ≤ 2.5 mg/day prednisolone: FRAX® may slightly overestimate risk
- 2.5–7.5 mg/day: FRAX® estimate is reasonably calibrated
- > 7.5 mg/day: FRAX® significantly underestimates risk — true fracture probability may be 15–20% higher than the FRAX® output
Some guidelines (e.g., ACR 2022) recommend adjusting FRAX® estimates upward by approximately 15% for patients on high-dose glucocorticoids (≥ 7.5 mg/day). Glucocorticoid-induced osteoporosis has a unique pathophysiology — it causes rapid bone loss (particularly cancellous bone) and direct osteocyte apoptosis, meaning that fractures can occur at higher BMD values than in postmenopausal osteoporosis.
This FRAX® input captures conditions that cause bone loss independent of the other listed risk factors. The specific conditions intended by FRAX® include:
- Type 1 (insulin-dependent) diabetes mellitus
- Osteogenesis imperfecta in adults
- Untreated long-standing hyperthyroidism
- Hypogonadism or premature menopause (< 45 years, untreated)
- Chronic malnutrition or malabsorption (including coeliac disease)
- Chronic liver disease
Important: Type 2 diabetes is not included as a cause of secondary osteoporosis in FRAX®, even though it is associated with increased fracture risk. This is because type 2 diabetes is paradoxically associated with higher BMD, and FRAX® may underestimate fracture risk in these patients. Rheumatoid arthritis has its own separate input and should not be double-counted under secondary osteoporosis.
FRAX® is validated only for femoral neck T-score, not lumbar spine, total hip, or other skeletal sites. The T-score should be derived from the GE Lunar, Hologic, or standardised sBMD reference. FRAX® uses the NHANES III young adult female reference range for both sexes.
- T-score ≥ −1.0: Normal BMD. Fracture risk is primarily driven by clinical risk factors.
- T-score −1.0 to −2.5: Osteopenia. FRAX® is particularly valuable here — many patients in this range have a high clinical fracture probability that warrants treatment.
- T-score ≤ −2.5: Osteoporosis by WHO definition. FRAX® helps quantify the magnitude of risk and guide treatment intensity.
When BMD is entered, FRAX® partially accounts for the effect of BMI on fracture risk through the BMD pathway. When BMD is not entered, BMI serves as a partial surrogate for bone density. This means the BMI adjustment is more influential in FRAX® without BMD than with BMD.
Pharmacological treatment for osteoporosis should be selected based on fracture risk level, comorbidities, patient preference, and prior treatment response. The general hierarchy follows international guidelines:
- Lifestyle measures (all patients): Weight-bearing and resistance exercise, adequate calcium (1000–1200 mg/day from diet ± supplements), vitamin D (800–1000 IU/day), smoking cessation, fall prevention strategies, limiting alcohol.
- First-line pharmacotherapy: Oral bisphosphonates (alendronate 70 mg weekly, risedronate 35 mg weekly) — well-established efficacy at hip, spine, and non-vertebral sites. Typically used for moderate-to-high risk.
- Parenteral bisphosphonate: Zoledronic acid 5 mg IV annually — for patients intolerant of oral bisphosphonates or with adherence concerns.
- Denosumab: 60 mg SC every 6 months — a RANKL inhibitor; effective across all sites. Consider for renal impairment (eGFR < 35) where bisphosphonates are contraindicated. Requires continuation without gaps due to rebound vertebral fractures on discontinuation.
- Anabolic agents (very high risk): Teriparatide (20 μg SC daily, max 24 months) or romosozumab (210 mg SC monthly, max 12 months) build new bone and are recommended first-line for very high fracture risk (e.g., FRAX® major ≥ 30%, multiple vertebral fractures, very low BMD). These should be followed by antiresorptive therapy to consolidate gains.
- HRT/Tibolone: May be considered for postmenopausal women under 60 or within 10 years of menopause, particularly if vasomotor symptoms are present.
Special Populations & Considerations
Trabecular Bone Score (TBS): TBS is a textural analysis of the lumbar spine DXA image that provides information about bone microarchitecture independent of BMD. It can be used as an adjustment to FRAX® (TBS-adjusted FRAX®), improving fracture prediction — particularly in patients with diabetes, glucocorticoid use, or osteopenia where standard FRAX® may underestimate risk. TBS adjustment is available in the official FRAX® tool.
Systematic Approach to Fracture Risk Assessment
Fracture risk assessment is recommended for: all postmenopausal women and men aged ≥ 50 with clinical risk factors, anyone with a prior fragility fracture, patients starting or already on glucocorticoids (≥ 3 months), patients with conditions causing secondary osteoporosis, and anyone with height loss > 2 cm or thoracic kyphosis suggesting vertebral fractures. Routine population screening without risk factors is generally not recommended before age 65 (women) or 70 (men).
Begin with FRAX® using clinical risk factors only (without BMD). This can be done in primary care without a DXA scan. The result will stratify the patient into a preliminary risk category. If the result clearly falls below the treatment threshold or clearly above it, the clinical decision may be straightforward. If the result falls near the threshold (the “intermediate zone”), proceed to DXA to refine the estimate.
If FRAX® without BMD yields an intermediate-risk result, arrange a DXA scan measuring femoral neck BMD. Recalculate FRAX® with the T-score. The result will be more precise and may shift the patient into a definitive treatment or reassurance category. This two-step approach avoids unnecessary DXA scans in clearly low-risk patients while ensuring high-risk patients are identified.
For patients above the treatment threshold: initiate pharmacotherapy, ensure adequate calcium and vitamin D, address modifiable risk factors, and arrange follow-up DXA in 3–5 years (or earlier if treatment response is uncertain). For patients below the threshold: provide lifestyle advice, address modifiable risk factors, and re-assess FRAX® in 3–5 years or when risk factors change. For intermediate-risk patients who decline treatment: shared decision-making, close monitoring, and reassessment within 2 years.
Common Pitfalls & Limitations
FRAX® is validated exclusively for femoral neck BMD T-score. Entering a lumbar spine T-score (which is often 0.5–1.0 SD lower due to degenerative changes or higher due to aortic calcification) will produce an inaccurate result. Similarly, total hip T-score, while clinically useful for diagnosis, is not the correct input for FRAX®. Always use the femoral neck T-score when entering BMD data.
If only a lumbar spine DXA is available, calculate FRAX® without BMD rather than using an incorrect site. The femoral neck was chosen for FRAX® because it is less affected by degenerative artefact and has the most extensive validation data linking it to fracture outcomes.
FRAX® uses binary (yes/no) inputs for risk factors that are in reality dose-dependent or graded. This means the algorithm cannot capture the full magnitude of risk in certain scenarios. Factors where FRAX® is known to underestimate include:
- Multiple prior fractures: FRAX® scores a single prior fracture the same as ten — yet recurrent fracture risk is substantially higher.
- Recent fracture: The “imminent fracture risk” in the first 2 years after a fracture is much higher than the 10-year average that FRAX® computes.
- High-dose glucocorticoids: > 7.5 mg/day prednisolone carries significantly higher risk than the average FRAX® glucocorticoid adjustment.
- Frequent falls: FRAX® does not include falls as an input, yet fall frequency is a major independent predictor of fracture.
- Type 2 diabetes: Fracture risk is elevated despite normal or high BMD.
Clinicians should apply clinical judgement to adjust the FRAX® result upward in these scenarios. Some guidelines provide specific correction factors (e.g., +15% for high-dose glucocorticoids).
FRAX® is validated for adults aged 40–90 only. Using it in patients under 40 (e.g., young adults on glucocorticoids) or over 90 is not recommended as the algorithm’s baseline hazard rates are not calibrated for these age groups. For younger patients, clinical judgement and specialist referral are more appropriate. For patients over 90, the competing mortality risk complicates 10-year probability calculations, and treatment decisions should focus on near-term risk reduction and quality of life.
FRAX® uses country-specific fracture incidence and mortality data. The same clinical profile will produce different 10-year probabilities depending on which country model is selected. Using the wrong country can substantially alter the result — for example, fracture rates in Scandinavia are approximately double those in some Mediterranean countries. Always select the country where the patient resides. If no specific model exists for the patient’s country of residence, use a surrogate country with similar fracture epidemiology (as suggested by FRAX® documentation).
FRAX® was developed and validated in untreated patients. Using it in patients already receiving anti-osteoporosis treatment (bisphosphonates, denosumab, teriparatide) will underestimate their untreated fracture risk — because their current BMD reflects treatment effect. This can lead to premature treatment discontinuation. FRAX® should not be used to decide whether to stop treatment. For monitoring treatment response, serial BMD and fracture incidence are more appropriate.
If FRAX® is required in a treated patient (e.g., for treatment review), consider using the pre-treatment BMD or calculating FRAX® without BMD using clinical risk factors alone.
Quick Reference Summary
| Risk Factor | FRAX® Input | Key Note |
|---|---|---|
| Age | 40–90 years | Primary driver of baseline fracture probability |
| Sex | Male / Female | Female sex associated with higher risk post-menopause |
| BMI | Auto-calculated | Low BMI increases risk; less influential when BMD is entered |
| Previous fracture | Yes / No | Strongest single risk factor; binary — does not capture number/recency |
| Parent hip fracture | Yes / No | Genetic component of fracture risk beyond BMD |
| Smoking | Yes / No | Current smoking only; former smoking not counted |
| Glucocorticoids | Yes / No | ≥ 5 mg prednisolone for ≥ 3 months; dose-dependent risk not captured |
| RA | Yes / No | Independent risk beyond glucocorticoid use; also proxy for T2DM risk |
| Secondary osteoporosis | Yes / No | Specific conditions only — see list above |
| Alcohol ≥ 3/day | Yes / No | Dose-dependent in reality; threshold set at ≥ 3 units/day |
| Femoral neck T-score | Optional | Femoral neck only — not lumbar spine or total hip |
FRAX® estimates fracture probability, not bone density. Treatment decisions should be based on the overall fracture probability — incorporating clinical risk factors — not on T-score alone. Use the official FRAX® tool with the correct country model for clinical decisions.
Disclaimer & References
For Educational Purposes Only. This calculator provides a simplified educational approximation based on published relative risks from FRAX® validation studies. It does not replicate the proprietary FRAX® algorithm and should not be used for clinical decision-making. For accurate fracture risk assessment, use the official FRAX® tool at frax.shef.ac.uk with the appropriate country model. Results should be interpreted in the full clinical context. This tool does not replace clinical judgement.
References
- Kanis JA, Johnell O, Oden A, Johansson H, McCloskey E. FRAX and the assessment of fracture probability in men and women from the UK. Osteoporos Int. 2008;19(4):385–397. DOI: 10.1007/s00198-007-0543-5
- Kanis JA, Harvey NC, Johansson H, et al. A decade of FRAX: how has it changed the management of osteoporosis? Aging Clin Exp Res. 2020;32(2):187–196. DOI: 10.1007/s40520-019-01432-y
- Kanis JA, Cooper C, Rizzoli R, Reginster JY. European guidance for the diagnosis and management of osteoporosis in postmenopausal women. Osteoporos Int. 2019;30(1):3–44. DOI: 10.1007/s00198-018-4704-5
- Cosman F, de Beur SJ, LeBoff MS, et al. Clinician’s guide to prevention and treatment of osteoporosis. Osteoporos Int. 2014;25(10):2359–2381. DOI: 10.1007/s00198-014-2794-2
- Compston J, Cooper A, Cooper C, et al. UK clinical guideline for the prevention and treatment of osteoporosis. Arch Osteoporos. 2017;12(1):43. DOI: 10.1007/s11657-017-0324-5
- Buckley L, Guyatt G, Fink HA, et al. 2017 American College of Rheumatology guideline for the prevention and treatment of glucocorticoid-induced osteoporosis. Arthritis Rheumatol. 2017;69(8):1521–1537. DOI: 10.1002/art.40137
- Leslie WD, Johansson H, McCloskey EV, Harvey NC, Kanis JA, Hans D. Comparison of methods for improving fracture risk assessment in diabetes: the Manitoba BMD cohort. J Bone Miner Res. 2018;33(11):1923–1930. DOI: 10.1002/jbmr.3538
- Kanis JA, Harvey NC, McCloskey E, et al. Algorithm for the management of patients at low, high and very high risk of osteoporotic fractures. Osteoporos Int. 2020;31(1):1–12. DOI: 10.1007/s00198-019-05176-3
- Camacho PM, Petak SM, Binkley N, et al. American Association of Clinical Endocrinologists/American College of Endocrinology clinical practice guidelines for the diagnosis and treatment of postmenopausal osteoporosis — 2020 update. Endocr Pract. 2020;26(Suppl 1):1–46. DOI: 10.4158/GL-2020-0524SUPPL