Osteoporosis Risk Score Calculator (OST Index)
The OST (Osteoporosis Self-Assessment Tool) is a validated screening score that uses only body weight and age to estimate the likelihood of low bone mineral density (BMD) in postmenopausal women. Enter your weight and age to get the OST index and a risk category.
Weight unit
years
Osteoporosis Self-Assessment Tool score — negative = higher risk
- 1
Weight − age
65 − 60 = 5 - 2
Multiply by 0.2
5 × 0.2 = 1 - 3
OST Index (truncate)
truncate(1) = 1Truncate rounds toward zero to the nearest integer, not to the nearest even.
How does this calculator work?
OST index = truncate[0.2 × (weight kg − age)]. Score < −1 is high risk for low bone density, −1 to 1 is moderate, above 1 is low risk. Validated in postmenopausal women as a quick triage before DXA scanning. High or moderate risk warrants a bone density scan.
Formula
How this is calculated
The Osteoporosis Self-Assessment Tool was developed and validated for postmenopausal women in Asian populations (Koh 2001) and has since been validated in diverse populations including Western European and North American women. It relies on just two readily available variables — body weight and age — and produces a single integer index.
A higher body weight relative to age raises the index (lower risk) because greater mechanical loading on bones promotes higher bone mineral density, and adipose tissue produces estrogen after menopause, which helps protect bone. Advancing age lowers the index (higher risk) because bone loss accelerates after menopause and with ageing.
Risk is categorised as: High (OST < −1), Moderate (−1 ≤ OST ≤ 1), and Low (OST > 1). Women in the high or moderate category are typically recommended for DXA (dual-energy X-ray absorptiometry) bone density scanning and further clinical evaluation. OST is a triage tool, not a diagnosis — the gold standard is DXA. Other important risk factors not captured by OST include family history of fracture, smoking, corticosteroid use, and previous fractures.
Frequently asked questions
A negative OST index — especially below −1 — suggests a higher probability of low bone mineral density (T-score ≤ −2.5 by DXA). Lower body weight and older age both push the index negative. It is a signal to discuss DXA scanning with a doctor, not a diagnosis of osteoporosis.
The OST was validated specifically in postmenopausal women. It has been studied in men with varying results; separate risk tools (such as MORES — Male Osteoporosis Risk Estimation Score) are considered more appropriate for males. The general pattern (higher weight, lower risk; older age, higher risk) still applies qualitatively.
Discuss a DXA scan with your healthcare provider. DXA measures bone mineral density at the lumbar spine and femoral neck and is the standard basis for diagnosing osteopenia or osteoporosis. Lifestyle measures — adequate calcium and vitamin D intake, weight-bearing exercise, not smoking — benefit bone health regardless of risk level.
Also known as
TG we-Calculate Editorial Team. (2026). Osteoporosis Risk Score Calculator (OST Index) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/osteoporosis-risk-score-calculator
TG we-Calculate Editorial Team. "Osteoporosis Risk Score Calculator (OST Index)." TG we-Calculate. 2026. https://we-calculate.com/calculator/osteoporosis-risk-score-calculator.
TG we-Calculate Editorial Team, "Osteoporosis Risk Score Calculator (OST Index)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/osteoporosis-risk-score-calculator
@misc{wecalculate_osteoporosis_risk_score_calculator, title = {Osteoporosis Risk Score Calculator (OST Index)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/osteoporosis-risk-score-calculator}}, year = {2026}, note = {TG we-Calculate} }
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