Fracture Risk Calculator
Estimate 10-year fracture risk using FRAX algorithm from age, BMD, and clinical risk factors. Enter values for instant results with step-by-step formulas.
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Risk is calculated using age-dependent baseline fracture rates modified by validated hazard ratios for each clinical risk factor. BMD T-score provides additional skeletal risk information. Treatment thresholds: Major fracture >= 20% or Hip fracture >= 3%.
Last reviewed: January 2026
Worked Examples
Example 1: Postmenopausal Woman with Risk Factors
Example 2: Male with Glucocorticoid Use
Background & Theory
The Fracture Risk Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the Fracture Risk Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Frequently Asked Questions
Formula
10-year fracture probability based on age, sex, BMI, clinical risk factors, and BMD T-score
Risk is calculated using age-dependent baseline fracture rates modified by validated hazard ratios for each clinical risk factor. BMD T-score provides additional skeletal risk information. Treatment thresholds: Major fracture >= 20% or Hip fracture >= 3%.
Worked Examples
Example 1: Postmenopausal Woman with Risk Factors
Problem: A 70-year-old woman with BMI 22, previous wrist fracture, mother who had hip fracture, and femoral neck T-score of -2.8. No smoking, no glucocorticoids, no alcohol excess.
Solution: Age: 70, Female, BMI: 22\nRisk factors: Previous fracture (RR 2.0), Parent hip fracture (RR 1.7)\nBMD T-score: -2.8 (Osteoporosis)\nBase hip risk adjusted for age: ~2.5%\nWith multipliers: 2.5 x 2.0 x 1.7 x BMD factor = ~14.5%\nMajor osteoporotic: ~28%
Result: 10-year hip fracture risk: ~14.5% | Major osteoporotic: ~28% | High Risk - Pharmacological treatment recommended
Example 2: Male with Glucocorticoid Use
Problem: A 60-year-old man with BMI 28, taking prednisolone 7.5mg daily for rheumatoid arthritis, no prior fracture, no family history, non-smoker, T-score -1.8.
Solution: Age: 60, Male, BMI: 28\nRisk factors: Glucocorticoids (RR 1.6), Rheumatoid arthritis (RR 1.5)\nBMD T-score: -1.8 (Osteopenia)\nBase hip risk adjusted for age: ~0.8%\nWith multipliers: 0.8 x 1.6 x 1.5 x BMD factor = ~3.2%\nMajor osteoporotic: ~12%
Result: 10-year hip fracture risk: ~3.2% | Major osteoporotic: ~12% | Moderate-High Risk - Treatment should be considered
Frequently Asked Questions
What is the FRAX fracture risk assessment tool?
FRAX is a fracture risk assessment tool developed by the World Health Organization (WHO) Collaborating Centre at the University of Sheffield to evaluate the 10-year probability of bone fracture in patients. It integrates clinical risk factors with or without bone mineral density (BMD) measurements to estimate the likelihood of hip fracture and major osteoporotic fracture. The algorithm was developed from population-based cohorts from Europe, North America, Asia, and Australia involving nearly 60,000 patients. FRAX is available in country-specific models for over 70 countries, accounting for the different fracture rates and mortality patterns observed across populations worldwide.
What risk factors does the FRAX algorithm include in its calculation?
The FRAX algorithm incorporates several well-validated clinical risk factors that independently contribute to fracture probability beyond bone density alone. These include age (40-90 years), sex, body mass index (BMI), prior fragility fracture, parental history of hip fracture, current smoking status, glucocorticoid use (prednisolone 5mg daily or equivalent for 3 or more months), rheumatoid arthritis, other causes of secondary osteoporosis, and alcohol intake of 3 or more units per day. An optional femoral neck BMD T-score can be entered to improve risk prediction accuracy. Each factor contributes independently to the risk calculation through validated hazard ratios.
What is the treatment threshold for fracture risk scores?
Treatment thresholds for fracture risk vary by country and clinical guideline but commonly used benchmarks include initiating pharmacological treatment when the 10-year major osteoporotic fracture risk exceeds 20% or the 10-year hip fracture risk exceeds 3%. The National Osteoporosis Foundation (NOF) in the United States recommends these thresholds based on cost-effectiveness analyses for the US healthcare system. Some countries use age-dependent intervention thresholds where the treatment threshold increases with age to match the average population fracture risk. The UK NOGG (National Osteoporosis Guideline Group) uses an age-dependent assessment threshold approach rather than fixed intervention thresholds.
How accurate is the FRAX tool at predicting individual fracture risk?
FRAX has been validated in multiple independent cohorts and demonstrates good calibration at the population level, meaning predicted and observed fracture rates are generally well-matched across risk categories. However, individual-level prediction is inherently uncertain because fracture is a stochastic event influenced by factors not captured in the model, such as fall frequency, fall mechanics, and bone microarchitecture quality. Studies have shown that FRAX tends to underestimate fracture risk in patients with multiple vertebral fractures, high-dose glucocorticoid use, or recent fractures within the past 2 years. For this reason, clinical judgment should supplement FRAX scores, particularly in patients with additional risk factors not included in the algorithm.
What is the difference between hip fracture risk and major osteoporotic fracture risk?
The FRAX algorithm provides two separate 10-year fracture probability outputs that serve different clinical purposes. The hip fracture risk represents the probability of sustaining a hip fracture specifically, which is the most devastating osteoporotic fracture with significant mortality (approximately 20% within one year) and morbidity. The major osteoporotic fracture risk encompasses the combined probability of fractures at the hip, spine (clinical vertebral fractures), forearm (distal radius), and proximal humerus, which together account for the majority of fracture-related healthcare burden. Treatment decisions are typically guided by both outputs, with most guidelines using the major fracture threshold of 20% or hip threshold of 3%.
How does age affect fracture risk calculations?
Age is one of the strongest independent risk factors for osteoporotic fracture, with risk increasing exponentially after age 50 in both men and women. For women, the 10-year hip fracture risk approximately doubles with each decade of age beyond 50, independent of bone density changes. This is because age affects fracture risk through multiple mechanisms including declining bone quality and microarchitecture, increased fall propensity due to sarcopenia and balance impairment, and reduced protective reflexes. The FRAX algorithm captures the independent effect of age on fracture risk beyond what is reflected in BMD measurements. However, FRAX is only validated for ages 40 to 90, and risk estimates outside this range should be interpreted with caution.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy