Can you bill Medicare before your enrollment is approved?

The rule, in the regulation’s own words

Two sections decide this and they have to be read together. 42 CFR 424.520(d) sets your effective date as the LATER of two things: the date you filed a Medicare enrollment application that was subsequently approved, or the date you first began furnishing services at the new practice location.

That word "later" is where the money goes. If you opened on 1 March and filed on 1 May, your effective date is 1 May — not March. Opening early does not start the clock; filing does.

Then 42 CFR 424.521(a) allows physicians, non-physician practitioners, physician and NPP organizations, physical therapists, occupational therapists and speech language pathologists to bill retrospectively for services furnished up to 30 days before that effective date, where circumstances precluded enrolling in advance. Up to 90 days if a Presidentially-declared disaster under the Stafford Act was the reason.

Source: 42 CFR 424.520 — effective date of billing privileges · 42 CFR 424.521 — retrospective billing

A worked example, because the arithmetic is the point

You see your first patient on 1 March. You file the CMS-855I on 1 May and it is approved.

Effective date: 1 May, the later of the two dates. Retrospective window: 1 April, thirty days before. Everything you did in March and the first days of April is not billable to Medicare, ever. Two months of Medicare work, written off, because of a filing date.

File before you open and the same two months are billable.

Source: 42 CFR 424.520 — effective date of billing privileges · 42 CFR 424.521 — retrospective billing

What "filing date" actually means

It is the date your MAC receives the application, not the date you started filling it in. CMS also states that a MAC will not fully process a PECOS application without the signature, the application fee where one applies, and the necessary supporting documentation.

So an application sitting in a MAC’s hands missing a signature is not doing the job you think it is doing. The practical read: submit complete, and treat anything returned for a missing document as though the clock never started.

Source: CMS — Medicare enrollment applications

Commercial payers do not work this way

There is no commercial equivalent of the 30-day look-back. A commercial contract generally pays from the effective date written into the countersigned participation agreement, and there is no federal rule obliging a plan to reach backwards at all.

That asymmetry is the single most expensive misunderstanding for a new practice: doctors reason from the Medicare rule they half-remember and assume the commercial plans will do something similar. They will not.