20 CFR § 330.3 - Daily rate of compensation.
(a) Definition. An employee's daily rate of compensation is his or her straight-time rate of pay, including any cost-of-living allowance provided in any applicable working agreement. It does not include any overtime pay, penalty payment, or other special allowance except as hereinafter provided. An employer's or employee's report of the daily rate of compensation shall, in the absence of information to the contrary, and subject to the considerations set forth in this section and §§ 330.4 and 330.5, be considered to show the daily rate of compensation of the employee by or for whom the report has been furnished. Where a rate other than a daily rate is reported, the Board will convert it to a daily rate.
(b) Hourly, weekly or monthly rate. An hourly rate shall be converted to a daily rate by multiplying such hourly rate by the number of hours constituting a working day for the employee's occupation or class of service. A weekly or monthly rate shall be converted to a daily rate by dividing such rate by the number of working days constituting the work week or work month, as the case may be, for the employee's occupation or class of service.
(c) Mileage rate. When a collective bargaining agreement provides for payment of compensation on a mileage basis, the employee's daily rate of compensation is his or her rate of pay for the number of miles constituting a basic day, including any allowance, as prescribed by the agreement, that is added to his or her basic rate of pay for the number of miles constituting a basic day.
(d) Piece rate or tonnage rate. Where a piece rate or tonnage rate is reported, the daily rate of compensation shall be determined by computing the employee's average earnings per day for the days on which he or she worked substantially full time (excluding any overtime pay or penalty rates) at such piece rate or tonnage rate during the last two pay periods in which he or she engaged in such work in the base year.
(e) Commissions or percentage of sales. Where the compensation reported consists of or includes commissions or percentages of sales, the daily rate of such commissions or percentage of sales shall be determined by computing the employee's average net commissions or percentage earnings (excluding any amounts he or she received to compensate him or her for expenses) per day for the days in the last two pay periods in which he or she worked on a commission or percentage basis in the base year.
(f) International service. In the case of an employee who, on his last day of employment in the base year, worked partly outside the United States and partly in the United States for an employer not conducting the principal part of its business in the United States, the employee's daily rate of compensation shall be determined in the same manner as it would if all his service on that day had been rendered in the United States.