Testosterone Free Calculator

Free Testosterone Calculator

Use this calculator to estimate your Free Testosterone (FT) levels based on your Total Testosterone, Sex Hormone Binding Globulin (SHBG), and Albumin levels. Free testosterone is the biologically active form of testosterone, not bound to proteins, and is readily available for use by the body's tissues.

Total Testosterone (ng/dL):

SHBG (nmol/L):

Albumin (g/dL):

Understanding Free Testosterone

Testosterone is a crucial hormone for men's health, playing a vital role in muscle mass, bone density, libido, mood, and energy levels. However, not all testosterone in your bloodstream is available for your body to use. Most of it is bound to proteins, primarily Sex Hormone Binding Globulin (SHBG) and, to a lesser extent, Albumin.

What is Free Testosterone?

Free testosterone is the portion of testosterone that is not bound to any proteins. It's the biologically active form, meaning it's readily available to bind to receptors in cells and exert its effects throughout the body. Levels of free testosterone are often considered a more accurate indicator of androgen status than total testosterone, especially when SHBG levels are abnormal.

The Role of SHBG and Albumin

Sex Hormone Binding Globulin (SHBG): This protein binds tightly to testosterone, making it unavailable for cellular uptake. High SHBG levels can lead to lower free testosterone, even if total testosterone is within the normal range. Factors like age, liver disease, thyroid disorders, and certain medications can influence SHBG levels.
Albumin: This is another protein that binds testosterone, but less tightly than SHBG. Testosterone bound to albumin is considered "bioavailable" because it can dissociate from albumin and become available to tissues. For the purpose of calculating "free" testosterone, albumin-bound testosterone is generally excluded.

Why Calculate Free Testosterone?

Measuring free testosterone directly in a lab can be expensive and technically challenging, often leading to less reliable results than calculated values. Therefore, calculating free testosterone using a formula that considers total testosterone, SHBG, and albumin is often preferred by clinicians. This calculation helps in diagnosing conditions like hypogonadism (low testosterone) or hyperandrogenism (high testosterone), especially when total testosterone levels are ambiguous or SHBG levels are abnormal.

How the Calculator Works

This calculator uses a widely accepted formula based on the law of mass action, often referred to as the Vermeulen method. This method accounts for the binding affinities of testosterone to SHBG and albumin to estimate the unbound (free) fraction of testosterone. The calculation involves solving a quadratic equation to determine the free testosterone concentration in molar units, which is then converted to more commonly used units like pg/mL and ng/dL.

Reference Ranges

Normal ranges for free testosterone can vary based on age, gender, and the laboratory performing the test. However, general reference ranges for adult males are often:

Free Testosterone: 50-200 pg/mL (or 5-20 ng/dL)

It's important to consult with a healthcare professional to interpret your results in the context of your overall health, symptoms, and other lab findings. This calculator provides an estimate and should not be used for self-diagnosis or to replace professional medical advice.

Example Calculation

Let's use the default values in the calculator:

Total Testosterone: 500 ng/dL
SHBG: 40 nmol/L
Albumin: 4.0 g/dL

Based on these inputs, the calculator would estimate your Free Testosterone to be approximately 79.44 pg/mL or 7.94 ng/dL. Note that slight variations in constants used by different calculators may lead to minor differences in results.

.calculator-container { font-family: 'Arial', sans-serif; background-color: #f9f9f9; padding: 20px; border-radius: 8px; max-width: 600px; margin: 20px auto; box-shadow: 0 2px 10px rgba(0,0,0,0.1); } .calculator-container h2 { color: #333; text-align: center; margin-bottom: 20px; } .calculator-input-grid { display: grid; gap: 15px; margin-bottom: 20px; } .calculator-input-row { display: flex; flex-direction: column; } .calculator-input-row label { margin-bottom: 5px; font-weight: bold; color: #555; } .calculator-input-row input[type="number"] { padding: 10px; border: 1px solid #ddd; border-radius: 4px; font-size: 16px; width: 100%; box-sizing: border-box; } .calculator-container button { background-color: #007bff; color: white; padding: 12px 20px; border: none; border-radius: 4px; font-size: 18px; cursor: pointer; width: 100%; box-sizing: border-box; transition: background-color 0.3s ease; } .calculator-container button:hover { background-color: #0056b3; } .calculator-result { background-color: #e9f7ef; border: 1px solid #d4edda; padding: 15px; border-radius: 4px; margin-top: 20px; font-size: 1.1em; color: #155724; text-align: center; font-weight: bold; } .calculator-result p { margin: 5px 0; } .calculator-article { margin-top: 30px; line-height: 1.6; color: #333; } .calculator-article h3, .calculator-article h4 { color: #333; margin-top: 20px; margin-bottom: 10px; } .calculator-article ul { list-style-type: disc; margin-left: 20px; margin-bottom: 15px; } .calculator-article li { margin-bottom: 5px; } function calculateFreeTestosterone() { var totalTestosterone_ng_dL = parseFloat(document.getElementById('totalTestosterone').value); var shbg_nmol_L = parseFloat(document.getElementById('shbg').value); var albumin_g_dL = parseFloat(document.getElementById('albumin').value); if (isNaN(totalTestosterone_ng_dL) || isNaN(shbg_nmol_L) || isNaN(albumin_g_dL) || totalTestosterone_ng_dL < 0 || shbg_nmol_L < 0 || albumin_g_dL < 0) { document.getElementById('result').innerHTML = 'Please enter valid positive numbers for all fields.'; return; } // Constants (from University of Sheffield calculator, widely cited Vermeulen method) var K_SHBG = 1.0e9; // L/mol var K_Alb = 3.6e4; // L/mol var Albumin_Molar_Mass = 66500; // g/mol var Testosterone_Molar_Mass = 288.42; // g/mol // 1. Convert inputs to molar concentrations (mol/L) var TT_nmol_L = totalTestosterone_ng_dL * 0.03467; // ng/dL to nmol/L var TT_mol_L = TT_nmol_L * 1e-9; // nmol/L to mol/L var SHBG_mol_L = shbg_nmol_L * 1e-9; // nmol/L to mol/L var Alb_g_L = albumin_g_dL * 10; // g/dL to g/L var Alb_mol_L = Alb_g_L / Albumin_Molar_Mass; // g/L to mol/L // 2. Solve the quadratic equation for Free Testosterone (FT) in mol/L // The equation is: K_SHBG * FT^2 + (1 + K_Alb * Alb_mol_L + K_SHBG * SHBG_mol_L) * FT – TT_mol_L = 0 // This is in the form a*x^2 + b*x + c = 0, where x = FT_mol_L var a = K_SHBG; var b = (1 + K_Alb * Alb_mol_L + K_SHBG * SHBG_mol_L); var c = -TT_mol_L; var delta = b * b – 4 * a * c; if (delta < 0) { document.getElementById('result').innerHTML = 'Error: Cannot calculate free testosterone with these values (discriminant is negative).'; return; } var FT_mol_L = (-b + Math.sqrt(delta)) / (2 * a); // Take the positive root // 3. Convert FT from mol/L to common units var FT_nmol_L = FT_mol_L * 1e9; // mol/L to nmol/L var FT_pg_mL = FT_nmol_L * Testosterone_Molar_Mass; // nmol/L to pg/mL (1 nmol/L = 288.42 pg/mL) var FT_ng_dL = FT_nmol_L * (Testosterone_Molar_Mass / 10); // nmol/L to ng/dL (1 nmol/L = 28.842 ng/dL) document.getElementById('result').innerHTML = 'Calculated Free Testosterone:' + " + FT_pg_mL.toFixed(2) + ' pg/mL' + " + FT_ng_dL.toFixed(2) + ' ng/dL'; }