Free Testosterone Calculator - Calculate Free & Bioavailable T

Enter your total testosterone, SHBG, and albumin from your lab results, get your free and bioavailable testosterone using the Vermeulen formula.

Free testosterone

Free & bioavailable T

Vermeulen calculation from total T, SHBG, and albumin.

SourceVermeulen et al. 1999 (JCEM)

Total testosterone

SHBG (nmol/L)

Albumin (g/dL, optional)

Free testosterone

113.1pg/mL

1.89% of totalReference range: 50–210 pg/mL (men, ages 20–49)

Bioavailable testosterone

275ng/dL

45.83% of totalReference range: 110–575 ng/dL (men)

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Calculated using Vermeulen et al. (1999 JCEM). For informational use only. Not a substitute for medical advice.

This calculator is for informational purposes only, so always double-check your result with a healthcare provider. It uses the Vermeulen et al. (1999 JCEM) formula, so results are estimates, not clinical measurements. We assume no liability for dosing errors.

The tool

How it works, what it tells you, what it doesn't.

Labs only report total testosterone, but most of it is bound to proteins and unavailable to your cells. The free testosterone calculator uses the Vermeulen 1999 JCEM formula to estimate what fraction is actually free and bioavailable. Enter your total testosterone (in ng/dL or nmol/L), SHBG (nmol/L), and albumin (g/dL, defaults to 4.3 g/dL if not on your panel). The calculator outputs free testosterone in pg/mL, free testosterone as a percentage of total, bioavailable testosterone in ng/dL, and bioavailable percentage. Useful for understanding why you may feel symptoms of low T even with a normal total testosterone number.

How to use it

How to Use the Free Testosterone Calculator

01

Find your lab results

You need total testosterone, SHBG (sex hormone-binding globulin), and optionally albumin. These are typically on a standard hormone panel.
02

Enter total testosterone

Enter in ng/dL or nmol/L, the calculator accepts both units. Typical male range is 300-1000 ng/dL.
03

Enter SHBG

Enter in nmol/L. Typical male range is 10-57 nmol/L. High SHBG means more of your testosterone is bound and unavailable.
04

Enter albumin (optional)

If your panel includes albumin (g/dL), enter it. Defaults to 4.3 g/dL, the population average, if left blank.
05

Read your result

The calculator shows free testosterone in pg/mL, free T as % of total, bioavailable testosterone in ng/dL, and bioavailable % of total, each with a reference range.

What Is Free Testosterone and Why Does It Matter?

Your total testosterone number tells you how much testosterone is in your blood. But roughly 98% of it is bound to proteins (SHBG and albumin) and unavailable to your tissues. Free testosterone is the 1-3% that is unbound and biologically active. Bioavailable testosterone includes free T plus the loosely albumin-bound fraction that can dissociate and become active.

This matters because two men with identical total testosterone levels can have very different symptoms if their SHBG levels differ. A man with total T of 600 ng/dL and high SHBG may have less free T available than a man with total T of 450 ng/dL and low SHBG.

Free Testosterone Reference Ranges by Age

Age Range	Low (pg/mL)	Normal (pg/mL)	Optimal (pg/mL)
20-29	< 9.3	9.3 - 26.5	15 - 26.5
30-39	< 8.7	8.7 - 25.1	13 - 25.1
40-49	< 6.8	6.8 - 21.5	11 - 21.5
50-59	< 7.2	7.2 - 24.0	10 - 24.0
60-69	< 6.5	6.5 - 18.1	9 - 18.1
70+	< 6.0	6.0 - 17.0	8 - 17.0

What Affects SHBG Levels?

Raises SHBG	Lowers SHBG
Aging	Obesity
Hyperthyroidism	Insulin resistance / Type 2 diabetes
Liver disease (cirrhosis)	Hypothyroidism
Estrogen therapy	Anabolic steroids
Anticonvulsants	High-dose corticosteroids

Understanding your SHBG is critical for interpreting testosterone levels. If your SHBG is high, your total T may look “normal” while your free T is genuinely low. This is one of the most common reasons men feel symptomatic despite having lab values within the reference range.

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Questions

Frequently Asked Questions

What is free testosterone and why does it matter?

Total testosterone includes testosterone bound to SHBG (tightly bound, inactive), testosterone loosely bound to albumin (partly available), and truly free testosterone (the biologically active fraction). Only free and albumin-bound testosterone can actually bind to androgen receptors. Men with high SHBG can have a normal total T but low free T, and feel the symptoms of low testosterone despite normal lab values.

What is the Vermeulen formula?

The Vermeulen et al. (1999) formula is the gold standard for calculating free testosterone from total T, SHBG, and albumin. Published in the Journal of Clinical Endocrinology & Metabolism, it's more accurate than simpler percentage estimates and is the method used by most endocrinologists and hormone specialists.

What is a normal free testosterone level?

Reference ranges vary by lab and age. Common ranges for adult men are approximately 50-210 pg/mL for free testosterone and 110-575 ng/dL for bioavailable testosterone (ages 20-49). These decline with age. The reference ranges shown in this calculator are for men aged 20-49.

Can I use nmol/L for total testosterone?

Yes, the calculator accepts both ng/dL and nmol/L. Use the unit selector next to the total testosterone input. To convert manually: nmol/L × 28.84 = ng/dL.

How does SHBG affect free testosterone?

SHBG is the main binding protein for testosterone. Higher SHBG leaves less testosterone free and bioavailable. SHBG rises with age, liver disease, certain medications (especially estradiol and thyroid hormones), and low BMI. Lowering SHBG, through interventions your doctor recommends, can increase free testosterone without changing your dose.