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Free Testosterone Calculator — with Bioavailable Levels

Table of contents

What is testosterone?Free testosteroneBioavailable testosteroneTestosterone levelsLow testosteroneHigh testosteroneTestosterone testHow to increase testosterone levels?

The bioavailable & free testosterone calculator is a tool that provides you with an estimation of free testosterone as well as bioavailable testosterone concentration. When you observe one of the problems with low libido, erections, fertility, or irregular menstruation, it indicates that you might have inappropriate testosterone levels, and you should definitely check them.

This calculator helps you see approximate testosterone fraction levels in your blood. In the article below, you will find out:

  • What testosterone is;
  • Why low testosterone is observed;
  • What are proper free testosterone levels;
  • How to do a testosterone test; and
  • How to increase testosterone levels.

What is testosterone?

Testosterone, by definition, is an organic compound, the primary male sex hormone, and an anabolic steroid. It is mainly produced in testicles by Leydig cells (♂) and also in small amounts by the adrenal cortex (♂/♀), ovaries (♀), and placenta (♀). Testosterone plays the leading role in the development of male reproductive organs like the testicles and prostate. It is also responsible for secondary sexual characteristics stimulation (building muscles, bone mass, growth of facial, pubic, and body hair, and deepening of the voice) — it literally turns boys into men. 🙂

Testosterone circulates in plasma in three forms: most of it is specifically bound to sex hormone-binding globulin (SHBG), another part is nonspecifically bound to albumin, and a small percentage is unbound.

Free testosterone

Free testosterone (FT) is a fraction of total testosterone (TT), which is not bound with any of the transport proteins (Albumin or SHBG). It is readily available for cells. FT measurements should be done when the TT test gives doubtful results. The test does not provide diagnostic value while fluctuations of SHBG level are too high.

The free testosterone norm depends on sex, age, and laboratory test methods.

Normal free testosterone levels:

  • For males: 50-210 ng/L (174-792 pmol/L); and
  • For females: <8.5 ng/L (<29.5pmol/L).

FT test is performed when the doctor suspects abnormal sexual development in boys. It is also suggested for males with libido/erection disorders and females with virilization symptoms.

Bioavailable testosterone

Bioavailable testosterone is more readily able to enter your cells and be used by your body — that's why this parameter is essential. It refers to the sum of free testosterone and albumin-bound testosterone.

Bioavailable testosterone = free testosterone + albumnin-bound testosterone

You could have the same total testosterone level as another male patient but a comparatively low index of bioavailable testosterone. Doing basic tests, where only total testosterone level is measured, might be confusing because you wouldn't understand why you had symptoms of testosterone deficiency while other men didn't. Getting complex measurements would give you a much more comprehensive picture of what is going on in your body.

Sometimes low testosterone might signal that something is going wrong in your body, and a dedicated treatment could be needed.

Testosterone levels

For males, 40%-60% of testosterone is bound with SHBG (strong binding). The rest binds to albumin (weak and reversible binding). Only 1%-4% of testosterone occurs as a free testosterone form (FT).

Your testosterone levels change hourly — the highest is in the morning, and the lowest is at night. They fluctuate with age as well. The highest level is around age 20-30, and then it slowly decreases.

Check your free testosterone levels using our calculator!

The equations used in this free testosterone calculator are based on Vermeulen Formulas, published in the article: "A Critical Evaluation of Simple Methods for the Estimation of Free Testosterone in Serum".

Testosterone levels may vary for many reasons. Usually, they drop and stay at a low volume. Less often, they grow too high. While this hormone is out of balance, health problems may occur. If you have any of the issues mentioned in the section below, ask your doctor about checking your testosterone levels. You can get treatment to fix hormone problems.

Normal levels of testosterone, according to sex and age are listed in the table below:


Male [ng/dL]

Female [ng/dL]

0-5 months



6 months to 9 years



10–11 years



12-13 years



14 years



15-16 years



17-18 years



19 years and up



If you are interested in other hormonal parameters like progesterone or estradiol and the balance between them, be sure to check our progesteron to estradiol calculator or testosterone to estrogen ratio tool.

Low testosterone

Low testosterone levels might cause a variety of symptoms in males, like:

  • Decreased sex drive;
  • Erectile dysfunctions;
  • Low sperm count;
  • Enlarged male breasts (gynecomastia);
  • Body hair loss;
  • Weight gain;
  • Weakness; and
  • Feelings of depression.

As a man gets older, testosterone production naturally decreases, but other factors can also cause hormone levels to drop. Injuries to the testicles and cancer treatments (chemotherapy, radiation) may unfavorably affect testosterone production. Negative influences also include stress and chronic diseases like AIDS, kidney diseases, alcoholism, and cirrhosis of the liver.

High testosterone

When young boys have too much testosterone, they can start puberty too early (before age 9). Some rare conditions, like certain types of tumors, cause boys to produce testosterone earlier than average. Sometimes too much testosterone results from Congenital Adrenal Hyperplasia (CAH). In some cases, it can cause men to have a very deep voice and women to grow facial hair. CAH can be diagnosed early in infants because of the symptoms — of dehydration and problems with feeding. It can also cause stunted growth and may even manifest with tall height in young men.

If you would like to learn more about the expected height of your child, visit our height calculator.

Testosterone test

To get testosterone levels checked, a blood test is required. The test should be performed in the morning, between 7-10 hours when testosterone levels are the highest. Females should complete the test in the first days of the menstrual cycle (2-5 days). Sometimes, the test needs to be retaken to confirm measurements.

While registering for the test, you should inform about any medicines you take.

Some medicaments (androgens and steroids) may decrease the concentration of testosterone.
Some may increase it:

  • Steroids (testosterone level can fall rapidly after stopping them);
  • Barbiturates;
  • Anticonvulsants; and
  • Estrogen therapies.

How to increase testosterone levels?

Are you considering testosterone therapy? Treatment is not necessary if your levels stay within the normal range. Testosterone replacement therapy is primarily beneficial for men with low testosterone levels. Do not take any testosterone supplements without consulting your doctor. They may cause side effects that are difficult to eliminate.

Prescription testosterone treatments are available as gels, skin patches, and intramuscular injections. Each of those medications comes with potential side effects (mood swings, skin irritation, etc.). Testosterone treatment is not advised for men with prostate or breast cancer.

Potential side effects of testosterone therapy might be:

  • Increased urination;
  • Increased acne;
  • Breast enlargement;
  • Decreased testicular size;
  • Decreased sperm count; and
  • Increased aggressive behaviors.

Doctors and researchers have varying opinions regarding the effectiveness of testosterone replacement therapy. Most agree that study results are mixed for most conditions.

Some food and herbs might help to boost your testosterone levels. These alternative and natural treatments aren't proven to be more or as effective as traditional testosterone therapy. Some may interact with any medications you take and cause unintended side effects!




Malaysian ginseng

Vitamin D


Pine bark extract

Dehydroepiandrosterone (DHEA)







Egg yolks

WARNING! This bioavailable and free testosterone calculator provides only estimations of testosterone fractions volume. Results from this calculator can NOT be considered as a basis for any medical decisions in any case/circumstance regarding diagnosis or treatment without prior consultation of a medical expert in this field. No responsibility is assumed for its correctness or suitability for any given purpose.

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