["The American Journal of Economics and Sociology, EarlyView. ", "\nABSTRACT\nThe proposal for a BRICS common currency lacks rigorous analytical treatment of which specific constraint makes it structurally inviable. This article applies a binding constraint methodology, adapted from Hausmann et al. (2008), to evaluate the institutional, financial, and geopolitical constraints confronting the BRICS common currency proposal under current international monetary architecture. Through structured focused comparison and counterfactual analysis, the article demonstrates that the financial convertibility and capital account constraint is binding: all five core BRICS members share an identical normalized Chinn‐Ito capital account openness score of 0.16, against a Eurozone founding‐member comparator of 0.82–1.00, placing the grouping uniformly in the bottom quartile of global capital account openness. Resolving institutional or geopolitical constraints alone cannot unlock monetary union viability; resolving the capital account constraint is necessary, though not sufficient, for viability to become conceivable. The article reframes the policy debate on BRICS de‐dollarization and contributes a structural corrective to the Eurozone analogy dominant in existing literature.\n"]