Professional liability is usually written on a claims-made or claims-made and reported basis, because a professional's error may not surface until years later. Occurrence forms exist but are exceedingly rare in this market.

Claims-made: the policy applies when the claim is first made during the policy period and the act happened on or after the retroactive date. Example: a malpractice policy runs from January 1, 2026 to January 1, 2027 with a retroactive date of January 1, 2022. In June 2026, two patients first make claims, one treated in March 2021 and one in March 2023. Only the 2023 treatment is covered. An act before the policy period is fine as long as it follows the retroactive date.

Claims-made and reported: two requirements. The claim must be made against the insured during the policy period, and it must also be reported to the insurer within that period or any reporting window the policy gives. An architect who receives a demand letter on December 20 but tells the insurer on January 10, after a December 31 expiration with no reporting window or tail, likely has no coverage.

California disclosure: Insurance Code §11580.01 applies to claims-made policies for professionals licensed under Division 2, or Chapter 4 of Division 3, of the Business and Professions Code. The application must state prominently at its heading that it is for a claims-made policy form. The face page of the policy must carry a conspicuous notice that coverage is generally limited to claims first made while the policy is in force.