Osteoporosis risk, explained
The Osteoporosis Self-assessment Tool (OST) estimates your risk of low bone density from just two numbers: (your weight in kg − your age in years) ÷ 5, keeping the whole number. The lower the score, the higher the risk, because older age and lower body weight are the two strongest simple predictors. For women, a score below 2 is the line commonly used to flag increased risk. About 1 in 2 women and up to 1 in 4 men over 50 will break a bone because of osteoporosis, so knowing your risk early matters.
Fracture figures: Bone Health & Osteoporosis Foundation. OST cut-off: USPSTF, 2025.
How this osteoporosis risk test works
- OST score. (Weight in kg − age in years) ÷ 5, with the decimal dropped (truncated toward zero). 62 kg at age 80 gives −3.6, so the score is −3.
- Women. A score below 2 means increased risk of low bone density; 2 or more means lower risk. This is the threshold the US Preventive Services Task Force lists as frequently used.
- Men. 4 or more: low · −1 to 3: moderate · −2 or less: higher. These bands come from one US study of 181 men (Adler 2003); the evidence in men is thinner.
- Second check for women (ORAI). Age points (45–54: 0, 55–64: 5, 65–74: 9, 75+: 15) + weight points (under 60 kg: 9, 60–69 kg: 3, 70 kg+: 0) + 2 if you are not taking estrogen. More than 8 points flags increased risk.
- Other risk factors do not change the score, because there is no published rule for adding them. A broken bone from a minor fall or long-term steroid medicine is a reason to ask about a bone density test whatever your score. A parent who broke a hip, smoking and heavy drinking are listed as extra risk.
Worked example. A 58-year-old woman who weighs 63 kg and does not take estrogen: OST = (63 − 58) ÷ 5 = 1, which is below 2, so increased risk. Her ORAI is 5 + 3 + 2 = 10 points, also above the 8-point line.
| Weight | Age 50 | Age 60 | Age 70 | Age 80 |
|---|---|---|---|---|
| 50 kg (110 lb) | 0 · increased · moderate | −2 · increased · higher | −4 · increased · higher | −6 · increased · higher |
| 60 kg (132 lb) | 2 · lower · moderate | 0 · increased · moderate | −2 · increased · higher | −4 · increased · higher |
| 70 kg (154 lb) | 4 · lower · low | 2 · lower · moderate | 0 · increased · moderate | −2 · increased · higher |
| 80 kg (176 lb) | 6 · lower · low | 4 · lower · low | 2 · lower · moderate | 0 · increased · moderate |
When should you get a bone density test?
The only way to diagnose osteoporosis is a bone density scan (DXA). In the US, the Preventive Services Task Force (2025) recommends screening for:
- All women aged 65 and older, whatever a risk score says.
- Postmenopausal women under 65 who are found to be at increased risk on a clinical risk assessment, such as the OST or ORAI.
For men, the Task Force found the evidence not yet strong enough to recommend for or against routine screening, so it is a decision to make with your doctor (USPSTF, 2025). These are US recommendations; screening rules differ between countries.
This test estimates the chance of low bone density, not the chance of a fracture. For a 10-year fracture probability, ask your doctor about a fracture risk tool such as FRAXplus.
How to protect your bones
- Load your bones. Weight-bearing exercise (walking, stairs, dancing) and muscle-strengthening on at least 2 days a week.
- Get enough calcium and vitamin D from food first, and ask your doctor before taking supplements.
- Don’t smoke and keep alcohol low. Both are on the list of risk factors in this test.
- Prevent falls. Strength and balance training lower the chance of a fall. Check your muscle strength with the muscle-loss test.
For women, bone loss speeds up after menopause; see the menopause timeline.
Osteoporosis risk FAQ
How is the OST score calculated?
Subtract your age in years from your weight in kg, divide by 5 and drop the decimal (truncate toward zero). A 70-year-old who weighs 60 kg scores (60 − 70) ÷ 5 = −2. An 80-year-old who weighs 62 kg gets −3.6, which becomes −3.
What OST score means high risk?
For women, a score below 2 is the threshold frequently used to define increased risk of low bone density (USPSTF, 2025). For men there is no agreed line; one US study used 4 or more as low, −1 to 3 as moderate and −2 or less as high risk (Adler 2003).
How accurate is the OST?
In 6,067 US women aged 50 to 64, a score below 2 picked up 62% of the women who had osteoporosis and correctly cleared 69% of those who did not (Zheng 2025). It works better for low bone density at the hip than at the spine. A 2025 review of 17 studies placed OST below 2 among the more sensitive, less specific screening tools (Wang 2025).
Does the OST predict fractures?
Only weakly. In 67,169 women aged 50 to 64, the OST was good at spotting low bone density at the hip but poor at predicting a major osteoporotic fracture over 10 years (Crandall 2023). For fracture probability, ask your doctor about a tool such as FRAX.
Why is there a second score (ORAI) for women?
ORAI adds whether you take estrogen (hormone therapy), which protects bone. Both ORAI and OST are recognised by the US Task Force. Above 8 points, ORAI found 53% of women with osteoporosis and correctly cleared 79% without it in the same study of 6,067 women (Zheng 2025).
Can this test diagnose osteoporosis?
No. It only estimates your risk of low bone density. A DXA bone density scan is needed to diagnose osteoporosis.
Who should be screened for osteoporosis?
In the US, all women 65 and older, and younger postmenopausal women who are at increased risk (USPSTF, 2025). For men, ask your doctor; the evidence for routine screening is not yet settled.
Can men get osteoporosis?
Yes. Up to 1 in 4 men over 50 will break a bone because of osteoporosis, according to the Bone Health & Osteoporosis Foundation. Low body weight, smoking, heavy drinking and steroid medicine raise the risk.
Last reviewed: · Sources · Educational estimate, not medical advice.
Sources
- Koh LK et al. A simple tool to identify Asian women at increased risk of osteoporosis. Osteoporosis International, 2001;12:699–705.
- Zheng HW et al. Identifying younger postmenopausal women with osteoporosis using USPSTF-recommended osteoporosis risk assessment tools. JAMA Network Open, 2025;8(3):e250626.
- US Preventive Services Task Force. Osteoporosis to prevent fractures: screening, final recommendation, 2025.
- Adler RA et al. Performance of the Osteoporosis Self-assessment Screening Tool for osteoporosis in American men. Mayo Clinic Proceedings, 2003;78:723–7.
- Crandall CJ et al. Race and ethnicity and fracture prediction among younger postmenopausal women in the Women's Health Initiative Study. JAMA Internal Medicine, 2023;183:696–704.
- Wang ST et al. Comparative accuracy of osteoporosis risk assessment tools in postmenopausal women: a systematic review and network meta-analysis. International Journal of Nursing Studies, 2025;165:105029.
- Bone Health & Osteoporosis Foundation. Osteoporosis fast facts.