What is GDP equal to in closed economy?

A closed economy (and there are extremely few) means complete self-sufficiency. A closed economy means there is no trade activity with outside economies, no exports, no imports. The remote unvisited tribe in unexplored Brazil is an example.

Brazil itself is relatively closed, exports plus imports equalled just 27.6 per cent of GDP in 2013. GDP measure the nation’s total income and the total expenditure on its output of goods and services.

Consumption (C) Investment (I) Government Purchases (G) Net Exports (NE) = exports minus imports plus net tourism. In a closed economy there are no net exports. Therefore C and I are what must be considered.