Idaho governs interest rates in the state through Title 28, Chapter 22 (Money of account and Interest) of Idaho Code. Section 28-22-104 of this Chapter prescribes the legal rate of interest as 12 percent per year, i.e., at the rate of twelve cents (12 cents) on the hundred by the year. A different rate of interest can be agreed upon in an express contract in writing.
Under Section 28-22-104 (2), the legal rate of interest on money due on the judgment of any competent court or tribunal is five percent plus the base rate which shall be the weekly average yield on U.S. Treasury securities as determined by Idaho state treasurer.
Idaho Code § 28-22-104
Legal rate of interest
(1) When there is no express contract in writing fixing a different rate of interest, interest is allowed at the rate of twelve cents (12 cent(s) ) on the hundred by the year on:
1. Money due by express contract.
2. Money after the same becomes due.
3. Money lent.
4. Money received to the use of another and retained beyond a reasonable time without the owner’s consent, express or implied.
5. Money due on the settlement of mutual accounts from the date the balance is ascertained.
6. Money due upon open accounts after three (3) months from the date of the last item.
(2) The legal rate of interest on money due on the judgment of any competent court or tribunal shall be the rate of five percent (5%) plus the base rate in effect at the time of entry of the judgment. The base rate shall be determined on July 1 of each year by the Idaho state treasurer and shall be the weekly average yield on United States treasury securities as adjusted to a constant maturity of one (1) year and rounded up to the nearest one-eighth percent (1/8%). The base rate shall be determined by the Idaho state treasurer utilizing the published interest rates during the second week in June of the year in which such interest is being calculated. The legal rate of interest as announced by the treasurer on July 1 of each year shall operate as the rate applying for the succeeding twelve (12) months to all judgments declared during such succeeding twelve (12) month period. The payment of interest and principal on each judgment shall be calculated according to a three hundred sixty-five (365) day year.
Idaho Code § 28-22-107
Consequences for failing to comply with requirements
No interest, collection costs and attorney’s fees shall be recovered on any dishonored check under the provisions of section 28-22-105, Idaho Code, where the holder of such check or any agent, employee or assignee of the holder has demanded:
(1) Interest or collection costs in excess of that provided in section 28-22-105, Idaho Code; or
(2) Interest or collection costs prior to the expiration of fifteen (15) days after the mailing of notice of dishonor, as provided in sections 28-22-105 and 28-22-106, Idaho Code; or
(3) Attorney’s fees, either without having such fees set by the court, or prior to the expiration of fifteen (15) days after the mailing of notice of dishonor, as provided in sections 28-22-105 and 28-22-106, Idaho Code.
The provisions of this section shall not prohibit the collection of a set collection fee which does not exceed twenty dollars ($ 20.00), if the holder has the right to collect a set fee under a written agreement or has notified the drawer at the point of sale that the drawer will be required to pay the set collection fee in the event a check is dishonored.
