<![CDATA[Purpose: This study examines the associations of tin prices and a Cost of Goods Sold (COGS)-based cost proxy with PT Timah Tbk’s Net Profit Margin (NPM) and evaluates the moderating role of the rupiah–US dollar exchange rate during 2018–2025. Research Method: The study uses a quantitative time-series design comprising 32 quarterly observations obtained from PT Timah Tbk, the London Metal Exchange, and Bank Indonesia. Daily tin prices and exchange rates were aggregated into quarterly arithmetic averages. Data were analyzed using descriptive statistics, diagnostic tests, multiple linear regression, and Moderated Regression Analysis in EViews 13. Results and Discussion: Tin prices are positively associated with NPM, whereas the COGS-based cost proxy has no statistically supported association with NPM. The interaction results provide insufficient evidence that the exchange rate moderates either relationship. Thus, insignificant interaction directions are not interpreted as strengthening or weakening effects. Implications: Management and investors should evaluate commodity-price movements alongside production volume, sales, cost composition, and foreign-currency exposure. The findings represent associations and do not establish causal or dominant determinants of profitability. Originality: This study integrates tin prices, reported costs, and exchange-rate interactions using recent quarterly data from an Indonesian tin-mining company.]]>
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