a safe bet
US /ə seɪf bet/
UK /ə seɪf bet/

1.
確実なこと, 安全な賭け
something that is certain to happen or to be successful
:
•
It's a safe bet that the new restaurant will be popular.
新しいレストランが人気になるのは確実だ。
•
Given his track record, he's a safe bet for the promotion.
彼の実績を考えると、昇進は確実だ。