The resource envelope represents the total financial resources available to a government during a fiscal year to finance its public expenditure program. It establishes the hard budget constraint within which the state must operate. It comprises domestic tax revenues, non-tax revenues, domestic and external borrowings, and international grants. Accurately forecasting the resource envelope is critical. Overestimating leads to mid-year fiscal crises and arbitrary spending cuts, while underestimating artificially restricts public investment.

Government revenues are legally and economically categorized into distinct streams:

The size and elasticity of the resource envelope depend directly on key macroeconomic variables. The Treasury tracks the Tax-to-GDP Ratio as a core metric of a country’s economic self-sufficiency. Other drivers include employment levels (driving income tax), consumer spending patterns (driving consumption taxes), and import-export volumes (driving customs duties).