How to Use the Free Testosterone Calculator
Choose the sex reference range, then enter total testosterone in ng/dL, SHBG in nmol/L, and albumin in g/dL. Ideally, use values from the same morning blood draw or assessment period.
The calculator solves a mass-action model and reports free testosterone, nmol/L equivalent, bioavailable testosterone, and free percentage.
Formula and Method - Free Testosterone Calculator
Total T = free T×(1 + Ka×albumin) + SHBG×Kshbg×free T ÷ (1 + Kshbg×free T)Testosterone circulates as free hormone, weakly albumin-bound hormone, and strongly SHBG-bound hormone. The model uses total testosterone, SHBG, albumin, and binding constants to infer free testosterone.
Use Cases for the Free Testosterone Calculator
- Estimating the effect of SHBG when total testosterone and symptoms do not align.
- Following changes in bioavailable testosterone as SHBG changes.
- Teaching why identical total testosterone can imply different free testosterone levels.