California Code, Labor Code - LAB § 5800

All awards of the appeals board either for the payment of compensation or for the payment of death benefits, shall carry interest at the same rate as judgments in civil actions on all due and unpaid payments from the date of the making and filing of said award. Such interest shall run from the date of making and filing of an award, as to amounts which by the terms of the award are payable forthwith. As to amounts which under the terms of the award subsequently become due in installments or otherwise, such interest shall run from the date when each such amount becomes due and payable.