GDP is an estimated value of the total worth of a country’s production and services, within its boundary, by its nationals and foreigners, calculated over the course on one year.
GDP = consumption + investment + (government spending) + (exports − imports)
Where as GNP is an estimated value of the total worth of production and services, by citizens of a country, on its land or on foreign land, calculated over the course on one year.
GNP = GDP + NR (Net income inflow from assets abroad or Net Income Receipts) - NP (Net payment outflow to foreign assets)