GDP和GNP的關係如下：
GNP = GDP + Factor Income From Abroad - Factor Income Paid Abroad首先同學要知道的是，假如一個經濟體系的所有國民都在本地生產，同時不容許別國國民在本地生產，則
GNP = GDPFactor Income From Abroad 指 本國國民在外的收入，Factor Income Paid Abroad 指 外國國民在本地的收入。若要計算國民的生產總值GNP，則必須從本地的生產總值中，加入國民在外所賺得的Factor Income From Abroad，同時減去非本國國民在本地生產所得的Factor Income Paid Abroad。等式可簡寫為
GNP = GDP + Net Factor Income From Abroad值得留意的是，Net Factor Income From Abroad 的別稱是Net External Factor Income Flow。
2013年Paper 1有一題問：
Which of the following items is NOT included in the calculation of Hong Kong's net factor income from abroad for the current year?
A. the income received by a Japanese teacher who worked in a language school in Hong Kong for one year
B. rental income earned from real estate holdings in Canada owned by a Hong Kong resident
C. salary received by an Indian consultant who worked for the Hong Kong Airport Authority for three months
D. dividends earned from shares in Hong Kong held by a US resident
答案是A。
D是美國國民在香港賺得的股息，股息是收入的一種。所以D屬於Factor Income Paid Abroad。
C是印度國民在香港賺得的收入，C屬於Factor Income Paid Abroad。
B是香港國民在加拿大賺得的租金收入，B是Factor Income From Abroad。
很多人不明白A不屬於Net factor income from abroad，因為對GNP的Resident身份不理解。GNP不計算Resident Producing Unit(常住生產單位)，而是國民(Resident)。Resident在經濟學的條件很簡單，某人在該經濟體系住滿12個月，或有意居住12個月，即被視為國民。這與其民族、膚色、血統無關。
A說日本老師在香港工作一年，直接被視為香港國民。雖然他是日本人，但已經成為Resident，直接是GNP的一部分。當然，他也是Resident Producing Unit，因為他的Centre of Interest是香港。
