Why Do Koreans Write 「며칠」 for “What Date,” Not 「몇 일」?

When a word starting with a vowel follows 「몇」 (myeot, “how many”), the final consonant ㅊ changes to a ㄷ (d) sound and carries over to the next syllable. So 「몇 월」 (what month) is pronounced [며둴] (myeo-dwol), 「몇 억」 (how many hundred million) [며덕] (myeo-deok), and 「몇 인분」 (how many servings) [며딘분] (myeo-din-bun).

By the same rule, 「몇 일」 should be pronounced [며딜] (myeo-dil). Yet when Koreans ask the date, they say [며칠] (myeo-chil), not [며딜]. Because the ㅊ (ch) sound stays alive, it is hard to see the word we use today as a combination of 「몇」 and 「일」 (il, “day”).

Since the neighboring words all start with 「몇」, as in 「몇 년 몇 월 몇 시」 (what year, what month, what hour), it is easy to think the date is also 「몇」 plus 「일」. The institute's commentary also notes that many people write 「몇 일」 because they assume 「몇」 is shared.

Some ask whether 「몇 일」 could be pronounced [면닐] (myeon-nil). But when 「일(日)」 meaning “day” of a date is attached, it is usually not pronounced [닐] (nil). It works like 「칠 일」 (the seventh day), which is pronounced [치릴] (chi-ril). Either way you reason, [며칠] does not come out.

Article 27 of Korea's Hangeul spelling rules says that a word formed from two words keeps each part's original form, but its Note 2 says words with unclear origins are not spelled in their original form. The example given there is 「며칠」. Listed alongside it are 「골병」 (golbyeong, deep-seated illness), 「골탕」 (goltang, a hard time), 「부리나케」 (burinake, in a hurry), and 「업신여기다」 (eopsinyeogida, to look down on).

「설거지」 (seolgeoji, washing dishes) is a similar case. Because the verb 「설겆다」 cannot be found in modern Korean, it is written as it sounds, 「설거지」, not 「설겆이」.

One common misconception is that 「몇 일」 is for asking the date and 「며칠」 is for talking about a span of days. The National Institute of Korean Language answers that it is always written 「며칠」, whatever the meaning. Both 「오늘이 며칠이에요?」 (What's the date today?) and 「며칠 동안 쉬었어요」 (I rested for a few days) use 「며칠」.

It also helps to remember the spacing. 「몇 월」 is two separate words, 「몇」 and 「월」, so it has a space, but 「며칠」 is a single word, so it is written together. So in a text or a form asking for a date, you can simply write 「몇 월 며칠」.