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.
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.
in one's interest
Also, in the interest of one; in one's own interest; in one's best interest. For one's benefit or advantage, as in It's obviously in their interest to increase profits, or Is this policy in the interest of the townspeople? or I suspect it's in your own best interest to quit now. [Early 1700s]