夜更(よふ)かしstaying up late, keeping late hours, sitting up late at night, nighthawk

昨日(きのう)夜(よ)更(ふ)かしをしたので、今日(きょう)は眠(ねむ)いです。

I stayed up late yesterday, so I'm sleepy today. {staying up late, keeping late hours, sitting up late at night, nighthawk}

試験(しけん)勉強(べんきょう)が終(お)わらなかったから夜(よ)更(ふ)かしをした。

I stayed up late because I hadn't finished studying for the exam. {staying up late, keeping late hours, sitting up late at night, nighthawk}

夜(よ)更(ふ)かしをしてしまった理由(りゆう)は、読書(どくしょ)に夢中(むちゅう)になっていたことだ。

The reason I stayed up late is because I was engrossed in reading. {staying up late, keeping late hours, sitting up late at night, nighthawk}

年越(としこ)しを除(のぞ)いて、子供(こども)達(たち)には夜(よ)更(ふ)かしをする事(こと)を禁止(きんし)しています。

Apart from New Year's Eve, we prohibit the children from staying up late. {staying up late, keeping late hours, sitting up late at night, nighthawk}

夜(よ)更(ふ)かしに限(かぎ)らず、お昼(ひる)や夕方(ゆうがた)までずっと寝(ね)ることも体(からだ)によくありません。

Not only staying up late, but also sleeping all the way until noon or evening is not good for your body. {staying up late, keeping late hours, sitting up late at night, nighthawk}