National income identity for an open economy
In a closed economy, there are three sources of demand for domestic goods – Consumption (C), government spending (G), and domestic investment (I).
We can write Y =C+ l + G
In an open economy, exports (X) constitute an additional source of demand for domestic goods and services that comes from abroad and therefore must be added to aggregate demand. Imports (M) supplement supplies in domestic markets and constitute that part of domestic demand that falls on foreign goods and services. Therefore, the national income identity for an open economy is
Y + M = C + I + G + X
Rearranging, we get
Y = C + I + G + X - M or
Y = C + I + G + NX
where, NX is net exports (exports – imports). A positive NX (with exports greater than imports) implies a trade surplus and a negative NX (with imports exceeding exports) implies a trade deficit.
