National income accounting measures aggregate economic activity, including GDP and its components. GDP is the total market value of final goods and services produced within a nation's borders in a given time period. GDP can be calculated by totaling expenditures on consumption, investment, government spending, and net exports. Alternatively, GDP can be viewed through the income approach by totaling wages, profits, interest, rent, and subtracting factors like depreciation and taxes to arrive at measures like national income and disposable personal income.