次第— The Moment It's Done

• 詳細が分かり次第、ご連絡いたします。

  Shousai ga wakari shidai, gorenraku itashimasu.

  As soon as the details are clear, I will contact you.

  Verb ます-stem 分かり + 次第 marks immediate action once details are known.

• 現地に到着次第、電話します。

  Genchi ni touchaku shidai, denwa shimasu.

  I'll call as soon as I arrive on site.

  Action noun 到着 + 次第 works directly without する for 'as soon as arriving'.

• 準備ができ次第、始めましょう。

  Junbi ga deki shidai, hajimemashou.

  Let's start as soon as preparations are ready.

  ます-stem でき + 次第 signals the next action begins the instant preparation ends.

• ・The main clause must be future/volitional — never a completed past event.
• ・Register: formal/business; polite emails favor it heavily.
• ・Don't confuse this time usage with 次第だ／次第で ('depending on').

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones 次第 is tested against.

• ～ないうちに — Before It Happens
• ～上(で) — After Doing / In the Process Of
• ～から～にかけて — Spanning From To
• ～際(に) — On The Occasion Of
• 最中に — Right in the Thick of It
• ～て以来 — Ever Since Then
• ～ところに／～ところへ — Right At That Moment
• ～ところを — Caught In The Act