-는 김에

while at it, since you're already doing it, on the occasion

Explanation

This expression is used when an action or state of affairs resulting from the action in the preceding clause becomes an opportunity to also do another originally unplanned but related action in the following clause.

Details

1. Even if the action expressed in the preceding clause happened in the past, this expression can be used in the present tense form -는 김에 as long as the action described in the following clause happened almost at the same time as the preceding action.

제 것을 사는 김에 동생 것도 하나 샀어요.
어제 방 청소를 하는 김에 부엌 청소도 했어요.

2. Even when expressing something occurring in the present, if the action in the preceding clause is completed before the action in the following clause begins, then the form -(으)ㄴ 김에 is used.

이렇게 다모인 김에 기념사진이나 찍을까요?
오랜만에 외출한 김에 분위기 좋은 곳에 가서 차나 한잔합시다.

While the expressions -(으)ㄹ 겸 -(으)ㄹ 겸 and -는 김에 are similar with respect to the fact that they indicate combining or doing together of two actions, they have the following differences.

Kimchi Reader

Expresses doing another action while doing something else, taking advantage of the situation.

Examples
시장에 가<span class='focus'>는 김에</span> 새로운 옷을 구경했어요.
Since I was going to the market anyway, I also browsed some new clothes.
모델 촬영을 준비하<span class='focus'>는 김에</span> 메이크업도 연습했어요.
While preparing for the modeling shoot, I also practiced my makeup.
서울에 오<span class='focus'>는 김에</span> 전시회에 들렀어요.
Since I came to Seoul anyway, I stopped by an exhibition.

16 more sentences in the app — free account.