に決きまっている

expression, ichidan verb

it's obvious that; it's bound to be; surely

Expresses strong conviction that something is naturally or inevitably the case. Often used in casual conversation. The speaker is certain about the outcome or state.

• そんなことを言いったら、彼かの女じょが怒おこるに決きまっている。

  If you say something like that, she's bound to get angry.

• 毎まい日にち練れん習しゅうすれば、上手じょうずになるに決きまっている。

  If you practice every day, you'll surely get better.