teggem@co.santa-barbara.ca.us,
Interest is due on awards and orders of the WCAB and courts per LC Sec 5800 you cite. See also the Code of Civil Procedure Sec 685.010, generally at10%, but for public entities at 7% per Government Code Sec 970.1(b) et seq.
You can use the Labor Code Book (Workers' Compensation Laws of California, Matthew Bender) Tables 5, 6 and 7 respectfully (I put a lot of work into the examples in Tables 5 and 6)
There is a formula for interest due over a number of days on page 2 of Table 4 in the commutation instructions which is very simple:
( value due times # of days between award and date paid) x .1/365
For 7% substitute .07 for .1! Try it and check it against the tables!