Mont. Code Ann. § 27-1-210

27-1-210 . Interest on torts. (1) (a) Subject to subsection (2), in an action for recovery on an injury as defined in 27-1-106 , a prevailing claimant is entitled to interest at a rate equal to the prime rate published by the federal reserve system in its statistical release H.15 Selected Interest Rates or in any publication that may supersede it on the day judgment is entered, plus 3%, on any claim for damages awarded that are capable of being made certain by calculation, beginning from the date 30 days after the claimant presented a written statement to the opposing party or the party's agent stating the claim and how the specific sum was calculated.

(b) The rate for bank prime loans established in subsection (1)(a) must be set as of January 1 of each year and remain in effect until December 31 of each year.

(2) The interest provisions of subsection (1) do not apply to damages not capable of being made certain by calculation, including but not limited to future damages until the damages are incurred and damages for:

(a) pain and suffering;

(b) injury to credit, reputation, or financial standing;

(c) mental anguish or suffering;

(d) exemplary or punitive damages;

(e) loss of established way of life;

(f) loss of consortium; and

(g) attorney fees.

(3) The jury is to be advised by the court that the court will determine the amount of prejudgment interest due, if any, on any judgment rendered.

(4) Any payment by a party of a claim or interest on a claim as set forth in subsection (1) is not an admission of liability and may not be made known to the jury.