What is the difference between Testosterone and Free Testosterone?

In the bloodstream, testosterone travels with the help of carrier proteins, which bind to it and release it when the body needs it. Total testosterone refers to the overall amount of testosterone in the blood, including both the portion attached to proteins and the small amount that remains free. Free testosterone is the active form; it’s not bound to proteins and makes up only about 2–5% of total testosterone. This form plays a key role in regulating mood, sex drive, muscle mass, and more.