Iowa Code § 573.5

Said bond shall run to the public corporation. The amount thereof shall be fixed, and the bond approved, by the official board or officer empowered to let the contract, in an amount not less than seventy-five percent of the contract price, and sufficient to comply with all requirements of said contract and to insure the fulfillment of every condition, expressly or impliedly embraced in said bond; except that in contracts where no part of the contract price is paid until after the completion of the public improvement the amount of said bond may be fixed at not less than twenty-five percent of the contract price.