From the CA DMV page.
Vehicle Registration and Title Information
How Vehicle Registration Annual Renewal Penalties are Calculated
Percentage of Vehicle License Fee + Registration Late Fee + CHP Late Fee = Total Due If payment is late: The penalty will be the sum of: Registration
Late Fee CHP $10
Late Fee $10
1-10 days* 10% of the vehicle license fee due for that year
10% of the weight fee due for that year, if any