When interest is due the contractor, all awarding public agencies, other than school districts, shall pay to the contractor interest at the rate of one and one-half percent (1 1/2%) per month of the final payment due the contractor. When interest is due to the contractor, school districts shall pay to the contractor interest at the rate of three fourths percent (3/4%) per month of the final payment due the contractor. For lump sum contracts the interest shall commence thirty (30) days after the work under the contract has been completed and accepted and all required material certifications and other documentation required by the contract have been furnished the awarding public agency by the contractor, and shall run until the date when the final payment or estimate is tendered to the contractor.

For contracts bid by unit prices the interest shall commence sixty (60) days after the above conditions are satisfied. When contract quantities or the final payment amount is in dispute, the interest-bearing period shall be suspended until the conclusion of arbitration and settlement of the dispute.