Tolong jawab pls!

Hi korang. Contoh firstday period 13/04/25 & lastday period 17/04/25. Then check upt +ve. Mcm mana nk kira usia kandungan kita berapa week tu? Nk kira lastday period tu kena mula dari 13hb tu atau yg 17hb tu?? Bantu jawab. Thankyou