て・
てすみません apologizes for something you or your side did, while なくてすみません apologizes for something you did not do. Use the past ending when looking back on a completed situation.
What the action phrase does
The verb before the apology identifies what you are sorry about. In context, that action should normally be something for which you, your group, or your organization is socially responsible. The construction is not merely stating a cause: its main purpose is to apologize.
Actions, omissions, and past incidents
First decide whether the regretted action happened. That determines whether you need the affirmative or negative form.
会議に遅れてすみません。
I'm sorry for being late to the meeting.
AnalyzeThe speaker was late, so the affirmative form is used.
昨日は連絡しなくてすみませんでした。
I'm sorry I didn't contact you yesterday.
AnalyzeThe speaker failed to make contact, so the negative form is required. The past ending looks back on yesterday's omission.
長い間お待たせしてすみません。
I'm sorry to have kept you waiting so long.
AnalyzeThis can be said when the waiting has just ended or while acknowledging the ongoing inconvenience.
A request versus an apology
A bare verb in the て-form can tell or ask the listener to do something in casual speech. Adding すみません instead looks toward the speaker's side and apologizes for an action.
More examples
何度も質問してすみません。
I'm sorry for asking so many questions.
Analyzeメールを確認しなくてすみませんでした。
I'm sorry I didn't check the email.
Analyze朝早く起こしてすみませんでした。
I'm sorry I woke you up early this morning.
Analyze約束の時間を間違えてすみません。
I'm sorry I got the meeting time wrong.
Analyze今日は手伝えなくてすみません。
I'm sorry I can't help today.
Analyze返事が遅くなってすみません。
I'm sorry for the late reply.
Analyze