in interest

in (one's) (own) interest

Beneficial to one. It would be in your interest to have your lawyer review the contract before you sign it.
See also: interest
Farlex Dictionary of Idioms.

in one's (own) (best) interest(s)

to one's advantage; as a benefit to oneself. It is not in your own interests to share your ideas with Jack. He will say that they are his. Jane thought it was in the best interest of her friend to tell his mother about his illness.
See also: interest
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • in (one's) (own) interest
  • in one's interest
  • in the interest of (one)
  • in the interest of
  • in (one's) best interest
  • declare an interest
  • declare an/(one's) interest
  • of interest
  • vested interest
  • in the interest of justice
References in periodicals archive
Life insurers began to ratchet up crediting rates on interest-sensitive policies in 2006, with a moderation in interest rate spreads.