A balanced budget (particularly that of a government) is a budget in which revenues are equal to expenditures. Thus, neither a budget deficit nor a budget surplus exists (the accounts "balance"). More generally, it is a budget that has no budget deficit, but could possibly have a budget surplus. A cyclically balanced budget is a budget that is not necessarily balanced year-to-year but is balanced over the economic cycle, running a surplus in boom years and running a deficit in lean years, with these offsetting over time.

Balanced budgets and the associated topic of budget deficits are a contentious point within academic economics and within politics. Some economists argue that moving from a budget deficit to a balanced budget decreases interest rates, increases investment, shrinks trade deficits and helps the economy grow faster in the longer term. Other economists, especially (but not limited to) those associated with Modern Monetary Theory (MMT), downplay the need for balanced budgets among countries that have the power to issue their own currency, and argue that government spending helps boost productivity, innovation and savings in the private sector.

Mainstream economics mainly advocates a cyclic balanced budget, arguing from the perspective of Keynesian economics that permitting the deficit to vary provides the economy with an automatic stabilizer—budget deficits provide fiscal stimulus in lean times, while budget surpluses provide restraint in boom times. Keynesian economics does not advocate for fiscal stimulus when the existing government debt is already significant.

Alternative currents in the mainstream and branches of heterodox economics argue differently, with some arguing that budget deficits are always harmful, and others arguing that budget deficits are not only beneficial, but also necessary.

Schools which often argue against the effectiveness of budget deficits as cyclical tools include the freshwater school of mainstream economics and neoclassical economics more generally, and the Austrian school of economics. Budget deficits are argued to be necessary by some within post-Keynesian economics, notably the chartalist school:

Budget deficits can be calculated by subtracting the total planned expenditure from the total available budget. This will then show either a budget deficit (a negative difference) or a budget surplus (a positive difference).

Modern Monetary Theory (MMT) is a school of thought founded by economist Bill Mitchell and Hedge Fund Manager Warren Mosler, and has since been further developed by economists such as Stephanie Kelton and L. Randall Wray. MMT advocates argue that a balanced budget is not required in the short term, or over the course of the business cycle in countries with monetary sovereignty, defined as follows:

A monetary sovereign is a country which: