Free Testosterone Calculator
Calculate free and bioavailable testosterone levels with SHBG and albumin
Testosterone Assessment
Normal range: 240-950 ng/dL (8.3-33.0 nmol/L)
Normal range: 10-57 nmol/L
Normal range: 3.5-5.0 g/dL (35-50 g/L)
Example Calculation
Adult Male Example
Input Values:
• Total Testosterone: 550 ng/dL (19.1 nmol/L)
• SHBG: 35 nmol/L
• Albumin: 4.3 g/dL
Calculated Results
• Free Testosterone: ~0.39 nmol/L (2.0%)
• Bioavailable Testosterone: ~8.2 nmol/L (43%)
• SHBG-bound: ~10.5 nmol/L (55%)
• Albumin-bound: ~7.8 nmol/L (41%)
Testosterone Fractions
Unbound, biologically active form
Weakly bound, easily dissociable
Strongly bound, not bioavailable
Free + albumin-bound testosterone
Normal Ranges
Males (Adult)
- • Total T: 240-950 ng/dL
- • Free T: 50-210 pg/mL
- • SHBG: 10-57 nmol/L
- • Albumin: 3.5-5.0 g/dL
Females (Adult)
- • Total T: 8-60 ng/dL
- • Free T: <8.5 pg/mL
- • SHBG: 18-144 nmol/L
- • Albumin: 3.5-5.0 g/dL
When to Test
Males - Symptoms:
- • Decreased libido
- • Erectile dysfunction
- • Fatigue and weakness
- • Depression or mood changes
- • Loss of muscle mass
Females - Symptoms:
- • Irregular menstruation
- • Hirsutism (excess hair)
- • Acne
- • Voice deepening
- • Balding pattern
Testing Guidelines
Optimal Testing Time:
- • Morning (7-10 AM) for males
- • Fasting not required
- • Avoid recent illness
- • Consider medication effects
For Females:
- • Days 2-5 of menstrual cycle
- • Before ovulation
- • Consider birth control effects
Understanding Testosterone Calculations
What is Free Testosterone?
Free testosterone is the fraction of total testosterone that is not bound to proteins and is immediately available for biological activity. It represents only 1-4% of total testosterone but is the most metabolically active form.
Bioavailable Testosterone
Bioavailable testosterone includes both free testosterone and testosterone loosely bound to albumin. This fraction (40-60% of total) can readily enter cells and exert biological effects.
Clinical Significance
- •Free testosterone may be more clinically relevant than total testosterone
- •SHBG levels affect testosterone availability
- •Age, obesity, and illness can alter SHBG and free testosterone
Vermeulen Formula
This calculator uses the validated Vermeulen equations to calculate free testosterone based on total testosterone, SHBG, and albumin concentrations. These formulas provide accurate estimates that correlate well with direct measurements.
Factors Affecting Results
Increase SHBG (↓ Free T)
Aging, hyperthyroidism, estrogen therapy, liver cirrhosis, HIV infection
Decrease SHBG (↑ Free T)
Obesity, insulin resistance, hypothyroidism, androgens, nephrotic syndrome
Important Clinical Notes
• Free testosterone calculations are estimates and may not reflect actual measured values
• Results should be interpreted in clinical context with symptoms and physical examination
• Normal ranges vary between laboratories and measurement methods
• Age-specific reference ranges should be considered for clinical interpretation
• Testosterone levels fluctuate throughout the day, being highest in the morning
! Medical Disclaimer
This Free Testosterone Calculator provides estimates based on validated mathematical formulas but cannot replace direct laboratory measurements or professional medical evaluation.
Important considerations:
- Calculated values are estimates and may differ from direct measurements
- Results should be interpreted by qualified healthcare professionals
- Clinical symptoms and examination are essential for proper diagnosis
- Normal ranges vary between laboratories and populations
- Treatment decisions should consider multiple factors beyond hormone levels
- Testosterone therapy has risks and requires medical supervision
This tool is intended for healthcare professionals familiar with hormone assessment and should not be used for self-diagnosis or self-treatment. Always consult with an endocrinologist or qualified physician for proper hormone evaluation and management.