Cal. Bus. & Prof. Code § 7141.5

The registrar shall grant the retroactive renewal of a license if, within 90 days of the expiration of the license, the otherwise eligible licensee submits a completed application for renewal on a form prescribed by the registrar, and pays the appropriate renewal fee and delinquency fee prescribed by this chapter. For the purposes of this section, an application shall be deemed submitted if it is delivered to the board’s headquarters or postmarked within 90 days of the expiration of the license.