Free Testosterone (Free T) Calculator
Enter your lab values below to estimate free testosterone and bioavailable testosterone using the Vermeulen equation.
Educational calculator only. Not a diagnosis. Always review hormone labs with a qualified clinician.
What is a free T calculator?
A free T calculator estimates the amount of testosterone in your blood that is not tightly bound to proteins. Most circulating testosterone is attached to proteins like SHBG (sex hormone-binding globulin) and albumin. A smaller fraction is “free,” and this value can provide extra context when total testosterone alone does not match symptoms or clinical picture.
This page gives you a simple, free testosterone calculator that uses total testosterone, SHBG, and albumin to estimate free T and bioavailable testosterone in seconds.
Why free testosterone matters
Total testosterone is useful, but it does not always tell the whole story. Two people can have similar total testosterone with very different SHBG values, and therefore very different free testosterone levels. That can make a big difference in interpretation.
- Total testosterone: the full amount in circulation
- Free testosterone: unbound fraction
- Bioavailable testosterone: free testosterone plus albumin-bound testosterone
Inputs used in this free testosterone calculator
1) Total Testosterone
You can enter total testosterone in ng/dL or nmol/L. The calculator automatically converts units internally.
2) SHBG
SHBG is entered in nmol/L. Higher SHBG generally reduces the free fraction of testosterone, while lower SHBG generally increases it.
3) Albumin
Albumin can be entered in g/dL or g/L. Albumin binds testosterone weakly, so it contributes to bioavailable testosterone calculations.
Method used: Vermeulen equation
This free T calculator uses a widely known mass-action model (Vermeulen approach) with standard association constants for testosterone binding to SHBG and albumin. It is a practical estimation method often used when direct equilibrium dialysis is not available.
Important caveats
- Lab assays and reference ranges vary.
- Clinical interpretation depends on age, sex, symptoms, medications, and health conditions.
- Calculated free T is an estimate, not a definitive diagnostic test.
How to use this calculator correctly
- Use fasting morning labs if possible (common clinical practice).
- Enter exact lab values with correct units.
- Click Calculate Free T.
- Review free T in both pmol/L and ng/dL, plus free % and bioavailable testosterone.
- Discuss results with your healthcare professional.
General interpretation context (not diagnostic)
Reference ranges differ by lab and population. The quick context below is only a rough orientation, not a medical threshold:
| Calculated Free T (pmol/L) | General Context |
|---|---|
| < 120 | Often below many adult male reference intervals |
| 120 - 220 | Lower range in many labs |
| 220 - 450 | Common mid-range zone in many labs |
| 450 - 700 | Upper-normal in many labs |
| > 700 | Often above many standard ranges |
Common mistakes when using a free T calculator
- Mixing units (for example, entering ng/dL as nmol/L).
- Using old or non-fasting values without context.
- Ignoring SHBG and albumin trends over time.
- Treating one number as a diagnosis instead of part of a full clinical assessment.
FAQ
Can women use this calculator?
Yes, the math works for any sex, but interpretation should be based on sex-specific reference intervals and clinical context.
Is calculated free T as accurate as direct lab measurement?
Direct methods such as equilibrium dialysis are often considered more definitive. Calculated free testosterone is a practical and commonly used estimate.
Why is SHBG so important?
SHBG strongly binds testosterone. Higher SHBG can reduce calculated free T even when total testosterone appears “normal.”
What if my result seems unexpected?
Re-check units, repeat labs under consistent conditions, and review with your clinician. Trends over time are often more informative than a single isolated value.
Bottom line
If you have total testosterone, SHBG, and albumin values, this free t calculator gives you a fast estimate of free testosterone and bioavailable testosterone. It is best used as a decision-support tool for informed conversations with a healthcare professional, not as a standalone diagnosis.