A transgender person’s legal gender changes when they change their gender marker legally.I know that sounds like a tautology or an unhelpful answer, but it’s the truth. Different jurisdictions have different legal standards for what must be done before a change of marker on documents, and sometimes those standards are VERY different.For example, each of the 50 US states has its own set of standards, including “gender cannot be changed”, for their documentation ‣ and sometimes it’s different for state ID card and birth certificate (the universally accepted proof of citizenship that must be provided to get a passport).The a federal standard to qualify for a gender marker change on your passport or social security records involves filing a standard DS-11 passport application form and including a medical certification. Federally, in the US, a medical certification is a letter written by your doctor stating that:He or she has a doctor/patient relationship with youHe or she has treated you or has reviewed and evaluated your medical historyYou have had, or are in process of having, appropriate clinical treatment for transition to the updated gender (male or female)The statement, “I declare under penalty of perjury under the laws of the United States that the forgoing is true and correct.” must also be included. The issuing doctor must be a DO (doctor of osteopathy) or MD, and is usually your primary care physician because of the treatment/evaluation requirement.The definition of “appropriate clinical treatment” in the federal standard (as of Nov 2023. is:Your physician determines what appropriate clinical treatment is according to acceptable medical practices, standards and guidelines, and certifies that you have had appropriate clinical treatment for gender transition to either male or female. Surgery is not a requirement to get a U.S. passport.Other countries or jurisdictions may well have quite different standards, including proof of specific surgeries or the submission of anatomical photographs.