I have seen 週一回 and 週に一回. I was wondering if anyone could explain the difference.


  • トレーニングは週2回です。
  • 週に一回ダンスを習っています。

I couldn't find an answer, I'm sorry this question has already been answered.


There is no difference in meaning, but the form without に only takes a pure unit with no number.

(× 二年一回/二年に一回)起こる。

(× 二週間一回/二週間に一回)起こる。

(一日二回/日【ひ】に二回/一日に二回)起こる。 ← a little irregular
(× 二日一回/二日に一回)起こる。

(一時間二回/× 時間に二回/一時間に二回)起こる。 ← 時間 would mean "time"
(× 二時間一回/二時間に一回)起こる。

  • Thank you for your clear explanation & examples! – JuliaJ Mar 31 at 8:31

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