"계산기를 잃어 버렸어" would be ok. FYI, 1) calculator : 계산기 (gye san gi) - kalkulator (计数器) 2) my calculator : 내 계산기 (nae gye san gi) - kalkulator saya(我的计数器) 3) to lose something: 잃다(ilh da), 잃어버리다 (ilh eo beo ri da) - hilang(丢) 4) lost something : 잃어버렸다.(ilh eo beo ryeot da) - sudah hilang(丢了) 5) I : 나는 (na neun) - saya(我) To sum up, (나는) (내) 계산기를 잃어버렸어. - (na neun) (nae) gye san gi reur ilh eo beo ryeoss eo. - saya sudah hilang kalkulator saya. - 我丢了我的计数器. "나는(subject)" and "내(possessive)" are left out because they are quite evident in the sentense.

More natual 나 계산기 잃어버렸어