Estimate free T from your labs.
Enter your total testosterone, SHBG, and albumin and Lumara estimates free and bioavailable testosterone with the Vermeulen equation — and shows the constants and the math. For tracking & education only; bring your results to your provider.
- SHBG–testosterone (Kt): 1.0×10⁹ L/mol
- Albumin–testosterone (Ka): 3.6×10⁴ L/mol
- Default albumin if blank: 4.3 g/dL
Lumara is a tracking tool and does not provide medical advice, diagnosis, or treatment. This calculator estimates free and bioavailable testosterone from the lab values you enter using the published Vermeulen equation; it does not interpret your results or recommend anything. Always discuss your labs with your provider.
Lumara keeps your labs and trends in one place so you and your provider can see the full picture over time. No values from this calculator are stored on this page.
The math stays here. The doses go in the app.
This calculator runs in your browser and saves nothing. In the Lumara app you log each dose your provider set, get reminders that fire on time, and in Premium track vial supply and use-by dates.
Free to download for iPhone & Android. Logging stays free for good; a 7-day trial of Premium runs in the app — no card. Tracking & education only, never a dose recommendation.
How to estimate free testosterone from your labs
Most testosterone in blood is bound to SHBG and albumin; only a small fraction is free. The Vermeulen equation estimates that free fraction from three lab values you already have on a report.
- Enter total testosterone in ng/dL or nmol/L from your lab report.
- Enter SHBG in nmol/L (sex hormone–binding globulin).
- Enter albumin in g/dL — or use the shown default if it is not on your panel.
- Read free and bioavailable T plus the free percentage, then discuss the numbers with your provider.
Worked example: total T 600 ng/dL, SHBG 30 nmol/L
A total testosterone of 600 ng/dL with SHBG 30 nmol/L and albumin 4.3 g/dL, via Vermeulen:
- Free testosterone — ≈ 12 ng/dL (about 2% of total).
- Bioavailable testosterone — ≈ 280 ng/dL (free plus the albumin-bound fraction).
- Why it matters — the same total T gives a lower free fraction when SHBG is high, and a higher one when SHBG is low.
These figures depend on your exact inputs and the assumed binding constants (shown in the tool). Reference ranges vary by lab — interpret any result with your provider.
Sources
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999;84(10):3666-72.
- Goldman AL, Bhasin S, Wu FCW, Krishna M, Matsumoto AM, Jasuja R. A reappraisal of testosterone's binding in circulation: physiological and clinical implications. Endocr Rev. 2017;38(4):302-324.
- Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744.
Frequently asked questions
Most testosterone circulates bound to SHBG (tightly) and albumin (loosely); the small unbound portion is free testosterone. Together, free plus albumin-bound is called bioavailable testosterone. The Vermeulen equation estimates these from total T, SHBG, and albumin.
It is a widely used formula that models how testosterone binds to SHBG and albumin to estimate the free fraction, using published association constants. It is an estimate — an equilibrium-dialysis lab measurement is the reference method. The tool shows the constants it uses.
Total testosterone in ng/dL or nmol/L, SHBG in nmol/L, and albumin in g/dL. If albumin is not on your panel, a normal default is commonly used. Use the exact values from your own lab report.
Reference ranges differ between labs and change with age, so this tool does not label a value normal or abnormal. It is an educational estimate, not a diagnosis — review your results with a licensed provider.
No. It estimates from the labs you enter and shows its work; it never diagnoses or recommends treatment. Always interpret lab results with your licensed provider.