Measuring GDP is complicated (which is why we leave it to the economists), but at its most basic, the calculation can be done in one of two ways: either by adding up what everyone earned in a year (income approach), or by adding up what everyone spent (expenditure method). Logically, both measures should arrive at roughly the same total.
Read more: What is GDP and why is it so important to economists and investors? http://www.investopedia.com/ask/answers/199.asp#ixzz3tkZKq1Al
Follow us: Investopedia on Facebook