Free Testosterone Calculator

Category: Fitness Author: Henrick Yau
- February 02, 2026
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Calculate your free testosterone levels using total testosterone, SHBG (Sex Hormone Binding Globulin), and albumin values. This calculator uses the Vermeulen equation for accurate estimation.

Patient Information

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Laboratory Values

Understanding Testosterone Levels

Testosterone circulates in the blood in three forms: free (unbound), albumin-bound, and SHBG-bound. Only free and albumin-bound testosterone (together called "bioavailable testosterone") are readily available to tissues.

Types of Testosterone
  • Free Testosterone (1-3%): Not bound to any protein and immediately available to tissues. This is the most biologically active form.
  • Albumin-bound (38-42%): Loosely bound to albumin protein. Can dissociate easily and is considered bioavailable.
  • SHBG-bound (55-60%): Tightly bound to Sex Hormone Binding Globulin. Not readily available to tissues.
Clinical Significance

Free testosterone is often more clinically relevant than total testosterone, especially in conditions that affect SHBG levels (obesity, diabetes, thyroid disorders, aging). Low free testosterone can cause symptoms even when total testosterone is normal.

Calculation Method

This calculator uses the Vermeulen equation, which is considered the gold standard for calculating free testosterone from total testosterone, SHBG, and albumin. It accounts for the binding affinities and concentrations of both SHBG and albumin.

Factors Affecting SHBG
  • Increase SHBG: Aging, hyperthyroidism, estrogen therapy, liver cirrhosis, anorexia
  • Decrease SHBG: Obesity, insulin resistance, hypothyroidism, androgen therapy, nephrotic syndrome
Medical Disclaimer

This calculator is for educational and informational purposes only. It does not constitute medical advice. Always consult with a qualified healthcare provider for interpretation of laboratory results and medical decisions. Laboratory reference ranges may vary between facilities.

\[ T_{\text{total}} = T_{\text{free}} + T_{\text{albumin-bound}} + T_{\text{SHBG-bound}} \] \[ T_{\text{bioavailable}} = T_{\text{free}} + T_{\text{albumin-bound}} \] \[ \text{Free \%} = \left(\frac{T_{\text{free}}}{T_{\text{total}}}\right)\times 100 \qquad \text{Bioavailable \%} = \left(\frac{T_{\text{bioavailable}}}{T_{\text{total}}}\right)\times 100 \] \[ \text{Method: Vermeulen equation (uses Total Testosterone, SHBG, and Albumin).} \]

What the Free Testosterone Calculator does

The Free Testosterone Calculator estimates how much testosterone in your blood is available for your body to use. It uses three lab results—total testosterone, SHBG (Sex Hormone Binding Globulin), and albumin—to estimate:

  • Free Testosterone: testosterone that is not attached to proteins and is ready for tissues to use.
  • Bioavailable Testosterone: free testosterone plus testosterone that is loosely attached to albumin.
  • Free % and Bioavailable %: the share of your total testosterone that is available.

The calculator applies the Vermeulen equation, a widely used clinical method for estimating free testosterone from standard lab values.

Why free testosterone matters

Total testosterone is a useful starting point, but it does not always reflect what your tissues can actually use. Proteins in the blood can bind testosterone and change how much is available.

  • SHBG-bound testosterone is tightly bound and usually not available to tissues.
  • Albumin-bound testosterone is loosely bound and can be used by the body, so it is counted as bioavailable.
  • Free testosterone is the most direct “available” form.

This is helpful when SHBG levels shift due to age, thyroid changes, weight changes, insulin resistance, or certain medications. In these cases, two people with the same total testosterone can have very different free testosterone results.

Who can benefit from this calculator

This tool can support informed conversations with a clinician when you want a clearer picture of hormone availability. It can be useful for:

  • People with symptoms that do not match their total testosterone result.
  • Anyone monitoring hormone therapy under medical care.
  • People who want to understand how SHBG may affect their results.
  • Those comparing results over time while keeping units consistent.

This calculator is educational. It does not diagnose a condition or replace medical evaluation.

What you need before you start

Have these lab values ready (from the same blood draw when possible):

  • Total Testosterone (common units: ng/dL or nmol/L)
  • SHBG (common units: nmol/L)
  • Albumin (common units: g/dL or g/L)

You will also enter:

  • Age
  • Biological sex (used for reference ranges and age-related comparison)

How to use the calculator step by step

  • Step 1: Enter your age.
  • Step 2: Select your biological sex.
  • Step 3: Enter your total testosterone and choose the correct unit (ng/dL or nmol/L).
  • Step 4: Enter your SHBG and choose the correct unit.
  • Step 5: Enter your albumin value and unit, or select Use default albumin (4.3 g/dL) if you do not have the lab result.
  • Step 6: Click Calculate Free Testosterone.
  • Step 7: Review the results, reference ranges, and charts.
  • Step 8: Use Reset to start over with new values.

How to read your results

After you calculate, the tool presents four headline results and two visuals.

  • Free Testosterone: your estimated unbound testosterone.
  • Bioavailable Testosterone: free plus albumin-bound testosterone.
  • Free %: how much of your total is free.
  • Bioavailable %: how much of your total is bioavailable.

Clinical interpretation and reference ranges

The interpretation section summarizes whether each result falls below, within, or above a reference range. The reference range table also shows your value next to typical ranges for men and women.

  • Use ranges as a guide, not a verdict. Labs can use different methods and ranges.
  • Focus on patterns. Compare results across time using the same lab when you can.
  • Pair numbers with symptoms. Lab values matter most with clinical context.

Charts: distribution and age-related comparison

The charts help you understand the “shape” of your testosterone results.

  • Testosterone Distribution (donut chart): shows the estimated split between SHBG-bound (unavailable), albumin-bound (bioavailable), and free (bioavailable).
  • Age-Related Comparison (line chart): compares your free testosterone to an age-based average curve for your selected sex.

These charts are for clarity and context. They do not replace a clinical assessment.

Tips for getting the most accurate inputs

  • Match timing: Use labs drawn at the same time of day when comparing results (testosterone can vary by time).
  • Use consistent units: Select the unit that matches your lab report before you calculate.
  • Prefer measured albumin: Use your actual albumin value if you have it. Use the default only when you do not.
  • Re-check outliers: If a result looks surprising, confirm the lab values and units first.

How this fits with Other-Health/">Other Health calculators

Hormones are one part of health. Many people also track nutrition and body composition. You can pair this tool with:

  • A Calorie Calculator for daily calorie intake, calorie requirements, and personalized calorie goals.
  • A BMI tool to check BMI and support a basic body mass index assessment.
  • A calculate BMR tool for a BMR estimate and daily calorie needs planning.
  • A body fat percentage or calculate body fat tool for a body composition check.
  • An ideal body weight or healthy weight range tool for weight assessment and weight management tool planning.
  • A calories burned estimate tool to track calorie burn and workout energy burn.

If you use several tools, look for consistent habits: sleep, training load, stress, nutrition tracker patterns, and medical follow-up when needed.

FAQ

What is free testosterone in simple terms?

Free testosterone is the portion of testosterone that is not attached to blood proteins. It is available for tissues to use right away.

What is SHBG and why does it matter?

SHBG is a protein that binds testosterone tightly. Higher SHBG often means less free testosterone, even when total testosterone looks normal.

What is bioavailable testosterone?

Bioavailable testosterone includes free testosterone plus testosterone loosely attached to albumin. Your body can access this portion more easily than SHBG-bound testosterone.

Can I use the default albumin option?

Yes. Use it if you do not have an albumin result. If you have albumin from the same lab draw, enter it for a better estimate.

Why do my free and total testosterone tell different stories?

Protein binding can change the available portion of testosterone. SHBG and albumin levels can shift with age, metabolic health, thyroid status, and some medications.

Does the calculator diagnose low testosterone?

No. It provides an estimate and a range comparison. A clinician should interpret results with symptoms, medical history, and repeat testing when needed.

What should I do if my result is outside the range?

Confirm the lab values and units first. Then discuss the results with a qualified healthcare provider, especially if you have symptoms or are on treatment.

Can women use this calculator?

Yes. The tool includes a biological sex selection and displays sex-specific reference ranges. Interpretation still depends on clinical context.

Important note

This calculator is for informational use. It can support understanding and better questions during a medical visit, but it cannot replace professional care. Reference ranges vary by lab, and any medical decision should come from a qualified healthcare provider.