次第です【しだいです】

次第です closes a formal explanation of how you came to do something: "that is why I…", "this is how it came about". It follows a plain-form verb, most often the た-form, since what you are explaining has already happened, and it belongs to business letters, emails, speeches and reports.

The sentence usually starts with the reason – a て-form, a ので clause, ため – and 次第です closes it on the action you took. The action is nearly always your own or your organisation's.

After a sentence that has already laid out what happened, というしだい次第です sums it up.

Non-past 次第です

With a humble verb of saying or asking, the non-past is a set way of offering thanks, an apology or a request.

次第です or わけです

わけです draws a conclusion from facts, about anyone, in any register. 次第です explains your own action and how it came about, and it only fits formal speech and writing. In conversation, say きごう〜たんです or というわけです.

• × 昨日寝坊して、遅刻した次第だよ → 昨日寝坊して、遅刻したんだ

次第 has other uses – "depending on" after a noun, "as soon as" after a ます-stem. Sentence-final 次第です after a verb is this one.