We cannot translate it by a word. Depending on the sentence, we need to change it. Let’s see with example sentences.


一日ずつ

いちにちずつ
ichinichi zutsu
  • どうぶつの森は、日にちを変えないで一日ずつやりましょう!
    doubutsunomori wa, hinichi wo kaenaide ichinichi zutsu yarimashou!

    You should play Animal Crossing day by day without changing the dates.
  • 一日ずつ。(しっかりと生きて行こう!)
    ichinichi zutsu. (shikkarito ikiteikou!)
    *inside the parenthesis is an implication.

    One day at a time.
    Un jour à la fois.

This phrase is not the only translation of ‘One day at a time’, however when I felt stressed about immigrating to Canada (to a French speaking area. I could not speak any French at all at that time.) and I cried, my mother-in-law gave me the phrase ‘Un jour à la fois’. In that situation, I understood that she said the sentence as I wrote above.


一日一歩

いちにちいっぽ
ichinichi ippo

one day one step

This is one of the 四字熟語 (よじじゅくご / yoji jukugo = Four character idiomatic compounds).

  • 一日一歩、成長していく。
    ichinichi ippo, seichou shiteiku.

    Growing (improving) day by day.

日に日に

ひにひに
hinihini
  • 歯医者さんの英語が、日に日に良くなっていますね!
    haisha-san no eigo ga, hinihini yokunatte imasune!

    Haisha-san(my beaver plush doll), your English is getting better day by day.
  • 親知らずのせいで、歯並びが日に日に悪くなる。
    oyashirazu no seide, hanarabi ga hinihini warukunaru.

    Because of the wisdom teeth, my teeth alignments get worse day by day.