-았/었더니 vs -더니

Intermediate · TOPIK II

-았/었더니 reports the speaker's own past action (first person) and then what they found or how others reacted; -더니 reports something the speaker observed about someone or something else (third person), followed by a change or what happened next.

-았/었더니An expression used to indicate that there is a new incident or situation, different from a past one.-더니A connective ending used when a certain fact or situation happened after a fact or situation in the past.

Rules of thumb

With -았/었더니 the first clause is usually 'I': 내가 …했더니 → the result I discovered.
-더니 usually has a third-person subject, the same in both clauses (동생이 …하더니 결국 …).
-더니 also contrasts past and present (어제는 춥더니 오늘은 따뜻하네요 'It was cold yesterday, but today it's warm').
Neither is followed by commands or suggestions; the second clause is usually something that already happened.
Don't use -더니 for your own actions (* 제가 열심히 공부하더니 …).

Example sentences

-았/었더니
When I opened the window this morning, it had snowed.
-더니
My little brother was coughing all morning, and in the end he got a fever.
-더니
It was so cold yesterday, but today it's warm.
-았/었더니
I called my friend, but they didn't pick up.
제가 열심히 공부하더니 시험에 합격했어요.
Incorrect
I studied hard and passed the exam. [Wrong: your own action doesn't take -deoni; use -ass/eotdeoni]

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