How to say "someday, sometime" in Russian?

"someday, sometime" is Когда-нибудь in Russian.

Когда-нибудь means "someday, sometime" in English.

Word #453 of 4,000 by frequency in Russian — level A1.

Когда-нибудь ты поймёшь, почему я так поступил.

Someday you'll understand why I did that.