A monthly fee that is never reconciled.
A client retains an agency for a hundred hours a month. In a quiet month the agency uses sixty. The fee is charged in full, the shortfall is described as capacity being held available, and the client has no way to know it happened because no agency reports hours against a retainer it has already banked.
Unused retainer is the most reliable margin in this industry. It requires no work, appears in no report, and accumulates in exactly the months a client is least likely to ask questions. Over a year it can amount to a fifth of the fee.
Agencies defend it as holding capacity, which is a real cost and a much smaller one than the unused fee. The honest version is a smaller retainer with an overage rate.
So we report hours against retainer every month and credit anything unused. Median utilisation across our book is 81%, which means roughly a fifth of what clients commit comes back to them. Last year that was about $214,000 of revenue we did not keep.
Unused retainer requires no work, appears in no report, and accumulates in the months a client is least likely to ask.