四よっ日か

よ

っ

か

Meanings

1

4th day of the month

Refers specifically to the fourth calendar day.

2

four days

Refers to a duration of four days.

〈事こと〉に四よっ日かかかる(something) takes four days
修しゅう理りに四よっ日かかかった。
The repair took four days.
四よっ日か前まえに〈動どう詞し〉to do something four days ago
四よっ日か前まえに東とう京きょうに着ついた。
I arrived in Tokyo four days ago.
〈時とき〉４よっ日かにon the 4th of a given month
３月がつ４日よっかに誕たん生じょう日びパーティーをした。
I had a birthday party on March 4th.

八よう日かN5
四日 (よっか, 'four days/the 4th') and 八日 (ようか, 'eight days/the 8th') are both irregular native-Japanese day readings that learners often mix up.
十じゅう四よっ日か
十四日 means the 14th (or 14 days) while 四日 means the 4th (or 4 days); the shared 四日 substring and irregular っか readings make them easy to misread.
五いつ日かN5
五日 (いつか) means the 5th day/five days, while 四日 (よっか) means the 4th day/four days—both share the same '〜か' day-name pattern and are easy to mix up.
三みっ日かN5
三日 (みっか) and 四日 (よっか) sit next to each other in the irregular series of native-Japanese day-readings, so learners often confuse which reading goes with which number.

Compound of 四 (yo, 'four') and 日 (ka, 'day'), with a geminate consonant shift yielding よっか.