If nominal GDP is, for example, \$1,620 billion in 2017 and increases to \$1,680 billion in 2018, is the growth rate 3.7%? Or does real GDP first need to be calculated using a deflator?
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As you pointed out, you need to distinguish between real and nominal GDP. The 3.7% growth from 1620 to 1680 is the nominal growth. To figure out real growth, you need to know the price index of the two years.