"How many days does it have been (since we started dating)?" =========================================== The suffix ~째 = ~th 첫째 딸 = first (eldest) daughter 뚤째 아들 = second son 셋째 자식 = third child I don't think there is a perfect match in English for 며칠째, but I think you know by now where it leads: 며칠째 = how many 'th' of day