Free Testosterone Calculator — Calculate Free & Bioavailable T
Enter your total testosterone, SHBG, and albumin levels from your blood work. This calculator uses the Vermeulen equation (the clinical standard used by ISSAM) to estimate your free and bioavailable testosterone with age-adjusted reference ranges.
Default 4.3 g/dL (normal)
What Is Free Testosterone and Why Does It Matter?
Your total testosterone number tells you how much testosterone is in your blood. But roughly 98% of it is bound to proteins (SHBG and albumin) and unavailable to your tissues. Free testosterone is the 1-3% that is unbound and biologically active. Bioavailable testosterone includes free T plus the loosely albumin-bound fraction that can dissociate and become active.
This matters because two men with identical total testosterone levels can have very different symptoms if their SHBG levels differ. A man with total T of 600 ng/dL and high SHBG may have less free T available than a man with total T of 450 ng/dL and low SHBG.
Free Testosterone Reference Ranges by Age
| Age Range | Low (pg/mL) | Normal (pg/mL) | Optimal (pg/mL) |
|---|---|---|---|
| 20-29 | < 9.3 | 9.3 - 26.5 | 15 - 26.5 |
| 30-39 | < 8.7 | 8.7 - 25.1 | 13 - 25.1 |
| 40-49 | < 6.8 | 6.8 - 21.5 | 11 - 21.5 |
| 50-59 | < 7.2 | 7.2 - 24.0 | 10 - 24.0 |
| 60-69 | < 6.5 | 6.5 - 18.1 | 9 - 18.1 |
| 70+ | < 6.0 | 6.0 - 17.0 | 8 - 17.0 |
What Affects SHBG Levels?
| Raises SHBG | Lowers SHBG |
|---|---|
| Aging | Obesity |
| Hyperthyroidism | Insulin resistance / Type 2 diabetes |
| Liver disease (cirrhosis) | Hypothyroidism |
| Estrogen therapy | Anabolic steroids |
| Anticonvulsants | High-dose corticosteroids |
Understanding your SHBG is critical for interpreting testosterone levels. If your SHBG is high, your total T may look "normal" while your free T is genuinely low. This is one of the most common reasons men feel symptomatic despite having lab values within the reference range.
Related Resources
- TRT Dose Calculator — calculate injection volume for testosterone cypionate and enanthate
- TRT Blood Work Guide — what labs to get and when
- Testosterone Cypionate Dosage Guide
- First TRT Injection: What to Expect
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For educational and research purposes only. This calculator provides estimates based on standard formulas.
Always verify calculations with your healthcare provider before use. We assume no liability for dosing errors, adverse events, or outcomes resulting from use of this tool.