This bill, named the "Fair Sentencing Act," aims to prevent federal courts from considering a defendant's perceived gender identity during sentencing. It specifically amends section 3553 of title 18, United States Code, to mandate that courts shall not use the perceived gender identity of a defendant as a mitigating factor, particularly when assessing history or rehabilitation. This change ensures that sentencing decisions are not influenced by an individual's self-identified gender. The legislation defines "perceived gender identity" as the self-identified gender identity of an individual, distinct from their biological sex. Furthermore, it directs the United States Sentencing Commission to amend its Guidelines Manual within 30 days of the Act's enactment to incorporate this prohibition, ensuring consistency across federal sentencing practices.