Expenditure approach
GDP = C + I + G + (X − M): personal consumption expenditures, gross private domestic investment, government consumption and gross investment, and net exports (exports minus imports). Imports are subtracted because their value was produced abroad.
Example: 20,000 + 5,000 + 5,000 + (3,000 − 4,000) = 29,000 (in any unit, such as billions).
Income approach
Gross domestic income (GDI) adds the incomes earned in production: compensation of employees + taxes on production and imports − subsidies + net operating surplus + consumption of fixed capital. In BEA's accounts, net operating surplus is proprietors' income, rental income of persons, corporate profits, net interest and miscellaneous payments, business current transfer payments and the current surplus of government enterprises.
In theory GDI equals GDP; in practice they are estimated from different data, and BEA reports the gap as the statistical discrepancy (GDP − GDI). With 15,000 compensation, 7,500 net operating surplus, 1,800 taxes, 100 subsidies and 4,800 depreciation, GDI = 29,000.
Real GDP and the deflator
Real GDP = nominal GDP ÷ deflator × 100, where the deflator is a price index equal to 100 in the base year. Nominal 29,000 with a deflator of 116 is 25,000 in base-year prices. The reverse, deflator = nominal ÷ real × 100, gives the price change since the base year. BEA's official real GDP uses chained dollars, so a single deflator is an approximation.