According to Okun’s law, for every 1 percentage point by which the actual unemployment rate exceeds the natural rate, a negative GDP gap of about 2 percent occurs. The actual unemployment rate exceeds the natural rate by 4 percent. This is calculated as follows :
Actual unemployment – natural unemployment = 9 – 5 = 4%.
Thus, according to Okun’s law the GDP gap is -8%.
If the potential GDP is $ 500 billion, the actual GDP is 8% lower than the potential GDP. In other words, 8% of the $ 500 billion is being forgone because of cyclical unemployment.
GDP forgone = 8% x potential GDP = 8% x 500 = $40 billion