Calculator inputs
Enter measured values, optional lab range, and sample details. Large screens use three columns, smaller screens use two, and phones use one.
Example data table
| Case | Sex | Age | Total T | SHBG | Albumin | Estimated Free T | Bioavailable T | Comment |
|---|---|---|---|---|---|---|---|---|
| Example A | Male | 30 | 520 ng/dL | 28 nmol/L | 4.4 g/dL | 116.23 pg/mL | 288.47 ng/dL | Typical working example with strong free fraction. |
| Example B | Male | 46 | 310 ng/dL | 42 nmol/L | 4.2 g/dL | 52.33 pg/mL | 124.22 ng/dL | Higher SHBG can reduce estimated free testosterone. |
| Example C | Female | 33 | 36 ng/dL | 90 nmol/L | 4.3 g/dL | 3.18 pg/mL | 7.72 ng/dL | Use laboratory-specific female reference intervals. |
Formula used
This page converts total testosterone into both ng/dL and nmol/L, normalizes albumin units, then estimates free and bioavailable testosterone from total testosterone, SHBG, and albumin.
- Total testosterone conversion: nmol/L = ng/dL × 0.0347
- Free androgen index: FAI = total testosterone in nmol/L × 100 ÷ SHBG
- Estimated free testosterone: solved from the law of mass action using total testosterone, SHBG, albumin, and binding constants
- Estimated bioavailable testosterone: free testosterone plus albumin-bound testosterone
- Percent free: estimated free testosterone ÷ total testosterone × 100
Calculated values are screening aids. They do not replace a laboratory report, equilibrium dialysis, or medical review.
How to use this calculator
- Select sex, age, and sample time.
- Enter the measured total testosterone result and choose the same laboratory unit.
- Enter SHBG and albumin values from the same blood draw when possible.
- Optionally add your lab’s lower and upper reference limits for tighter flagging.
- Choose symptom severity to add contextual notes in the result section.
- Press Calculate levels to show results above the form.
- Use the CSV or PDF buttons to save the displayed summary.
Frequently asked questions
1. What does this calculator estimate?
It estimates total testosterone in two units, calculated free testosterone, bioavailable testosterone, percent free, and the free androgen index using entered lab values.
2. Why is SHBG included?
SHBG binds testosterone strongly. Higher SHBG can lower estimated free testosterone even when total testosterone appears acceptable on the laboratory report.
3. Why does albumin matter?
Albumin binds testosterone weakly. That weakly bound fraction is often considered bioavailable, so albumin changes the free and bioavailable estimates.
4. Is free testosterone measured or calculated here?
This page calculates it from total testosterone, SHBG, and albumin. Direct laboratory methods and equilibrium dialysis may give different results.
5. Why is morning collection mentioned?
Morning testing is commonly preferred for adult men because testosterone shows daily variation. Timing can change interpretation, especially near cutoff values.
6. Can women use this calculator?
Yes, but female reference intervals vary more by laboratory and assay. Enter your laboratory range for more useful interpretation notes.
7. Does a low result confirm hypogonadism?
No. Diagnosis usually considers symptoms, repeat testing, timing, medications, illness, and sometimes additional hormones such as LH, FSH, or prolactin.
8. Are the export buttons saving my data online?
No. The CSV and PDF exports are created in your browser from the displayed result summary on the page.