How long does it take for an acl injury to fully heal?

It does not heal: An acl ligament tear does not heal on its own. When an acl tears, the fluid inside the knee seals off the two torn ends of the acl and prevents them from coming back together. Because of this, it can never really heal. You can feel better because the rest of the knee calms down, but the acl will remain torn. A reconstructed acl takes about 8 months for the body to reincorporate.

Usually doesn't.: If you've torn your ACL, it usually does not heal itself. The swelling from the injury may go down, but you're still left with a torn ACL. See an ortrhopedic sports medicine knee surgeon, who can advise you if surgery is needed.