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.
Do the math once. Let the app do it forever.
Estimated free T 12 ng/dL · Total T 600 · SHBG 30 · Alb 4.3. Save this vial and dose to Lumara and every future draw is pre-computed — with reminders that fire on time and expiry tracking, all on your device.
Free to download for iPhone & Android. A 30-day trial runs in the app — no card — then it stays free for one medication. 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.
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.