PEPFAR Extension Act of 2018 This bill amends the United States Leadership Against HIV/AIDS, Tuberculosis, and Malaria Act of 2003 to extend certain provisions related to the U.S. President's Emergency Plan for AIDS Relief (PEPFAR), a U.S. governmental initiative addressing the global HIV/AIDS epidemic. Specifically, the bill extends through FY2023 provisions that: require the Inspectors General of the Department of State and the U.S. Agency for Global Media, jointly with the Department of Health and Human Services and the U.S. Agency for International Development, to coordinate and conduct oversight of PEPFAR programs; limit U.S. contributions to the Global Fund to Fight AIDS, Tuberculosis and Malaria to 33% of funds contributed from all sources; require that certain fund contributions be withheld under specified circumstances; require that at least half of the PEPFAR budget be allocated for specified HIV/AIDS treatment and care; and require that at least 10% of such budget be expended for assistance to orphans and other children. The bill also extends through FY2024 annual reporting requirements relating to HIV/AIDS treatment providers and costs.