Self-executing — the payer owes it automatically
Under Labor Code §4603.2/§4622, California WC penalty and interest are self-executing: a payer that pays late owes them by operation of law, no request required. Medical-legal bills: 10% penalty + 7% simple interest after the 60-day EOR deadline. Treatment e-bills: 15% penalty + 10% interest after 45 days (private payer) or 60 days (governmental). Interest accrues from the date the payer received the bill — not from the deadline.
Compute what you're owed
Open /wizard/penalty-interest, pick the bill type, enter the unpaid amount and the received/paid dates. The calculator flags whether the deadline was breached and totals unpaid + penalty + interest. Mindbill auto-adds penalty & interest to the expected reimbursement on a late-paid bill and surfaces them on the Second Review, so you never leave that money on the table.