Guaranteed to get or have, as in We're in for a difficult time. [Late 1500s]
in for it. Certain to encounter trouble or punishment, as in When Harry finds out we left early, we'll be in for it. [Late 1600s]
Involved or entered for some purpose, as in We're in for the profits. [Mid-1800s] Also see have it in for; in for a penny.
|certain to get or have; "he knew he was in for a licking"|