29 C.F.R. § 4.172
Where a fringe benefit determination specifies the amount of the employer's contribution to provide the benefit, the amount specified is the actual minimum cash amount that must be provided by the employer for the employee. No deduction from the specified amount may be made to cover any administrative costs which may be incurred by the contractor in providing the benefits, as such costs are properly a business expense of the employer. If prevailing fringe benefits for insurance or retirement are determined in a stated amount, and the employer provides such benefits through contribution in a lesser amount, he will be required to furnish the employee with the difference between the amount stated in the determination and the actual cost of the benefits which he provides. Unless otherwise specified in the particular wage determination, such as one reflecting collectively bargained fringe benefit requirements, issued pursuant to section 4(c) of the Act, every employee performing on a covered contract must be furnished the fringe benefits required by that determination for all hours spent working on that contract up to a maximum of 40 hours per week and 2,080 (i.e., 52 weeks of 40 hours each) per year, as these are the typical number of nonovertime hours of work in a week, and in a year, respectively. Since the Act's fringe benefit requirements are applicable on a contract-by-contract basis, employees performing on more than one contract subject to the Act must be furnished the full amount of fringe benefits to which they are entitled under each contract and applicable wage determination. Where a fringe benefit determination has been made requiring employer contributions for a specified fringe benefit in a stated amount per hour, a contractor employing employees part of the time on contract work and part of the time on other work, may only credit against the hourly amount required for the hours spent on the contract work, the corresponding proportionate part of a weekly, monthly, or other amount contributed by him for such fringe benefits or equivalent benefits for such employees. If, for example, the determination requires health and welfare benefits in the amount of 30 cents an hour and the employer provides hospitalization insurance for such employees at a cost of $10.00 a week, the employer may credit 25 cents an hour ($10.00 ÷ 40) toward his fringe benefit obligation for such employees. If an employee works 25 hours on the contract work and 15 hours on other work, the employer cannot allocate the entire $10.00 to the 25 hours spent on contract work and take credit for 30 cents per hour in that manner, but must spread the cost over the full forty hours.
29 C.F.R. § 4.172