California workers'-comp law does something unusual and powerful: it makes penalty and interest on late payments self-executing. Under LC §4603.2 (treatment) and LC §4622 (medical-legal), a payer that pays late owes the penalty and interest automatically — you don't have to ask for it, and the payer doesn't get to decide whether to apply it. If they paid late, they owe it. Period.
The two rate tiers
The amount depends on the type of bill and, for treatment bills, the type of payer:
| Bill type | Penalty | Interest | Deadline that triggers it |
|---|---|---|---|
| Medical-legal | 10% | 7% simple | After the 60-day EOR deadline. |
| Treatment (e-bill, private payer) | 15% | 10% | After 45 days. |
| Treatment (e-bill, governmental payer) | 15% | 10% | After 60 days. |
Interest accrues from the date the payer received the bill — not from the deadline — so the longer they sit on it, the more it compounds in your favor.
Self-executing means automatic. You don't file anything to "earn" penalty and interest on a late med-legal bill. The obligation arises by operation of law the day the payment is late. The only thing you have to do is calculate it correctly and make sure the payer actually included it.
The 60-day med-legal deadline
For medical-legal bills, the key date is 60 days. The payer must issue an EOR and pay within 60 days of receiving a properly documented med-legal bill (8 CCR §9792.5). Miss that window, and two things happen at once:
- The 10% penalty + 7% interest begin to accrue automatically; and
- The failure to issue a timely EOR becomes its own violation, supporting a DWC audit complaint under
LC §4622 / §129.5.
In other words, a payer who blows the 60-day deadline owes you more money and exposes themselves to an audit complaint. That combination is your leverage.
Why most shops miss it
Penalty and interest get left uncollected for one reason: nobody is tracking the received-date and the deadline on every bill, then re-checking each payment to confirm the penalty and interest were actually included. Payers frequently pay the principal and quietly omit the penalty and interest, betting you won't notice. On a single bill it's small; across hundreds of late payments a month it's real money — and it's money the law already says you're owed.
Make it mechanical
The fix is to treat penalty and interest as a standing line item on every late payment: record when the payer received the bill, watch the 45/60-day clock, and when a payment lands late, compute the amount due and demand it (and file the audit complaint on day 61 when no EOR has come at all). Because it's self-executing, you're not asking for a favor — you're collecting a statutory obligation the payer already incurred.
This guide is general information for California workers'-comp and med-legal billers, not legal advice. Statutes, fee schedules, and forms change — confirm against the current DWC regulations for your dates of service.