Four Agency Billing Models and the Unbilled Work Most Firms Miss

Agency invoices must satisfy clients, procurement, and the agency's own cash flow, and most problems stem from unstated rules. The article outlines four billing approaches: retainers billed in advance or arrears, milestone or fixed fees, and time-and-materials. It stresses that each invoice should tie directly to a contract clause or an approved deliverable, with approval details recorded. Pass-through costs should be billed at cost on separate lines with supporting third-party invoices, and any markup agreed upfront. The piece also flags the unbilled work agencies often overlook, along with client-specific invoicing requirements that should be documented once and reused.