This work introduces The Coherence Equation, a unifying physical law that links coherence directly to measurable resources: time, energy, and information. The framework formalizes the Coherence Budget Principle, stating that coherence is sustained only within the limits of these resources and collapses once the budget is exceeded. The equation provides a clear operational foundation for understanding superposition, entanglement, and interference as economic phenomena rather than paradoxes. It unites the behavior of quantum systems under a single resource-based rule, offering predictive power and direct experimental applicability. This version reflects the updated formulation and structure of the framework, including its role as both a theoretical law and a practical tool for experimental and applied physics Version note: This version replaces all previous drafts and releases of The Coherence Equation (previously published as Energy–Information Principle Framework). Earlier license terms do not apply to this version. Any academic, applied, or commercial use must refer to the current license and framework as published in this releas