計GDP方法有3:
Expenditure Approach (支出面）- 講得淺易啲係喺街收單加埋哂啲支出，去計一個經濟體內RPU嘅最終產出，點解咁emphasize 係喺街收單?想你記緊default佢係市價，題目鍾意要學生轉factor cost，就要減稅加津貼還原
Expenditure Approach 裡面已分好哂類，category 就係大家背得好熟嘅C+I+G+X-M，C=Consumption 同G=Government Expenditure 喺考題上變化唔大，稍要格外留神係唔好當錯transfer payment 係G，失業救濟、生果金、綜緩金都只係左手交右手，唔涉生產，不計算入GDP
考得最刁鑽要數I=Investment ，買一手樓、起廠、買一手機器、商戶庫存等全部都係Investment，連帶衍生嘅acquisition cost，包稅包佣都係入I，而I 嘅變化選好多端：
- GROSS INVESTMENT 喺計GDP條或個G就係GROSS INVESTMENT
- GROSS DOMESTIC CAPITAL FORMATION 與 GROSS INVESTMENT 完全EQUIVALENT
- GROSS DOMESTIC FIXED CAPITAL FORMATION 見FIXED要加CHANGE IN INVENTORY
- NET DOMESTIC FIXED CAPITAL FORMATION 見NET要加DEPRECIATION 見FIXED要加CHANGE IN INVENTORY
- NET INVESTMENT 見NET要加DEPRECIATION
X-M (Net Export)要計齊export 加re-export再減import，減import嘅原因係因為前邊C/I/G/X等有機會有進口成份。雖然要包re-export，但考局鍾意同時出齊total export value同re-export俾你，其實前者已包後者，唔使額外再加
