Direct tariff incidence captures only the visible portion of supply-chain exposure because industries with limited or no direct imports may still inherit tariff burden through upstream suppliers. This paper develops the Tariff Exposure Propagation Index (TEPI), an industry-month measure of hidden tariff exposure transmitted through inter-industry production linkages. TEPI combines HS-10 tariff incidence, monthly U.S. import data, an HS-to-NAICS-to-BEA crosswalk, and the Bureau of Economic Analysis Industry-by-Industry Total Requirements matrix to decompose exposure into direct incidence, propagated incidence, and a snapback-adjustment term for post-reversal recovery dynamics. The empirical panel covers 71 BEA Summary-level industries from January 2023 onward using public U.S. government data sources. During the 2025–2026 IEEPA tariff shock period, the mean applied tariff rate reached 12.46 percent across $29.2 trillion in imports. Forty-six industries, or 65 percent of the sample, recorded zero direct tariff exposure but non-zero TEPI driven entirely by upstream propagation. Wholesale trade ranked second in the economy by total TEPI despite having zero direct incidence, while professional, financial, transportation, utility, and infrastructure-service industries exhibited similar hidden-exposure patterns. TEPI extends conventional tariff-incidence analysis beyond imported goods and provides a reproducible, open-source evidence base for sourcing analysis, supplier-risk prioritization, and scenario planning under volatile trade-policy conditions.