Wash. Admin. Code § 458-28-020
"Gross income of the business" means the value proceeding or accruing by reason of the transaction of the business engaged in and includes gross proceeds of sales, compensation for the rendition of services, gains realized from trading in stocks, bonds, or other evidences of indebtedness, interest, discount, rents, royalties, fees, commissions, dividends, and other emoluments however designated, all without any deduction on account of the cost of tangible property sold, the cost of materials used, labor costs, interest, discount, delivery costs, taxes, or any other expense whatsoever paid or accrued and without any deduction on account of losses.
Other examples of gross income are receipts from carrying charges, service charges, credit cards, safety deposit box rentals, bookkeeping or data processing, overdraft fees, flooring fees, and penalty fees.
Wash. Admin. Code § 458-28-020
Order ET 72-1, § 458-28-020, filed 9/29/72.