V + (ㄴ) 지 얼마나 됐어요? can be used when asking how long it’s been since you started doing or last did something:
한국에 온지 얼마나 됐어요?
How long has it been since you came to Korea?
한국에 온지 여섯 달 됐어요.
It’s been six months since I came to Korea.
일본에 이사한지 얼마 안 됐어요.
It hasn’t been that long since I moved to Japan.
농구를 한지 오래 됐어요.
It’s been a while since I played basketball.
우리를 만난지 오래 됐어요.
It’s been a while since we met.
여기서 일한지 얼마나 됐어요?
How long have you worked here?
밥을 먹은 지 3시간 됐어요.
It’s been three hours since I last ate.
결혼한지 얼마나 됐어요?
How long have you been married?
결혼한지 3년이 됐어요.
I’ve been married for about 3 years.
한국말을 배우기 시작한 지 일곱 달 됐어요.
It’s been seven months since I started learning Korean.
여기서 산 지 얼마나 됐어요?
How long have you lived here?