はず

The word はず can be used after a phrase or sentence to express that you expect something to be the case, based on your knowledge or memory of the subject. It can translate as "supposed to", "should", "I expect that" or "I believe that..."

It can be negated in two ways: ないはず or はずがない. The negation sounds stronger with the latter, and can also mean that something is inconceivable.

あの映画は面白いはずだよ。映画専攻の友達が３回も観たって言ってたから。
That movie's supposed to be interesting. My friend who studies movies said he'd seen it three times.

リーさんが毎日納豆を食べられるなら、賞金を取るはずってんだよ。
Lee-san said that if you can eat natto every day, you're supposed to win a prize.

今月の家賃を払ったはずなのに、大家さんにまだもらっていないと言われた。変だなあ。
Even though I believe I paid the rent for this month, the landlord told me they still haven't gotten it. It's strange.

おやつとかジュースとか持ったから、赤ちゃんは大丈夫はずだよ。
I brought things like snacks and juice, so the baby should be fine.