Form 5472 Reference ID Number: What It Is and How to Assign One

Form 5472 has to identify the related parties on each side of a reportable transaction. Normally a party is identified by a US taxpayer identification number — an EIN for a company or an SSN/ITIN for an individual. But the typical related party on a foreign-owned LLC’s Form 5472 is a non-resident owner with no US number at all. The reference ID number solves that: it is a stand-in identifier the filer assigns so the IRS can still recognize and track that party.

The reference ID appears on the line for the foreign shareholder’s identifying number in Part II, and again wherever the related party is identified. The owner’s foreign tax ID (for example, a Brazilian CPF or an Indian PAN) is reported on its own separate line — it does not replace the reference ID. You provide both: the foreign tax ID and the US-style reference ID you created.

There is no application and no waiting — you simply decide on an identifier and use it. The IRS rules are about format and consistency, not about getting permission. The practical goal is an identifier that is unique to that related party and that you can reproduce identically every year.

A practical convention

Most single-owner LLCs have exactly one related party, so a simple scheme works well: take the LLC’s EIN, add a dash, and append 001 for the first related party (98-7654321-001). If you ever add a second related party, use -002, and so on. This keeps the identifier tied to the LLC, easy to reproduce, and obviously unique. To see it placed on an actual form, the /form-5472-example/ page shows the reference ID in Part II of a completed sample.

This is the situation nearly every foreign-owned single-member LLC is in. The non-resident owner has never been issued a US taxpayer number — they have no SSN (that requires work authorization), often no ITIN (which is for individuals with a US filing requirement of their own), and no personal EIN. With no US-issued number to enter, the form would otherwise have a blank where the owner’s identifier should be. The reference ID number fills that gap.

Do not confuse the reference ID with the owner’s home-country tax number. Form 5472 asks for both: the foreign taxpayer identification number from the owner’s country, and a reference ID number you assign. They sit on different lines and serve different purposes — the foreign tax ID is the owner’s real overseas number; the reference ID is the consistent internal handle the IRS uses to match the party across filings.

The IRS gives you latitude on the exact format, which can paradoxically cause anxiety — founders worry they will pick the “wrong” one. There is no wrong format as long as it is alphanumeric, within 50 characters, free of disallowed special characters, unique to the party, and used consistently. Pick something systematic and stick with it.

Whatever convention you choose, write it downand keep it with the LLC’s records so next year’s filing uses the identical identifier. A small ledger of “related party → reference ID” prevents the most common error: accidentally inventing a new ID the following year.

Consistency is the whole point of the reference ID. The IRS uses it to recognize that the “Maria Silva” on your 2025 Form 5472 is the same related party as the one on your 2026 and 2027 forms. If you assign 98-7654321-001 one year and 98-7654321-002 the next for the same owner, the system can read that as two different parties — exactly the confusion the reference ID exists to prevent.

A genuinely new identifier is appropriate only for a genuinely new related party. As long as the owner is the same person, the reference ID never changes. This is one of several small technical details — alongside the pro forma 1120 notation and the correct filing method — where a careless inconsistency can turn an otherwise correct filing into one the IRS flags. Keeping these details right across years is part of what the flat $299 service handles, especially for filers catching up on multiple years at once.

It is worth drawing the line clearly, because the three are easy to conflate. An EINis the LLC’s own IRS-issued employer identification number, used in Part I. An ITIN is an IRS-issued individual taxpayer number that some non-residents obtain for their own US filing needs. The reference ID number is neither — it is an identifier you make up for a related party that lacks any US number.

So the LLC still needs a real EINto file at all — that is non-negotiable and comes from the IRS. The reference ID does not substitute for the LLC’s EIN; it only stands in for the foreign owner’s missing US number. For how the LLC and owner fit together on the form, see /foreign-owned-disregarded-entity/ and the line-by-line /form-5472-instructions/.

Most foreign-owned single-member LLCs have exactly one related party: the foreign owner. But some structures have more — for instance, the owner plus a foreign parent company, or the owner plus a sibling company they also control. The rule is straightforward: each related party that engaged in a reportable transaction gets its own Form 5472, and each gets its own distinct reference ID number. You do not list multiple parties on one form; you file one Form 5472 per related party.

How to number multiple parties

Keep the EIN-based convention and increment the sequence. If the LLC’s EIN is 98-7654321, the owner might be 98-7654321-001, a foreign parent company 98-7654321-002, and an affiliated foreign sibling company 98-7654321-003. The first three digits of the sequence stay tied to the same LLC, so every reference ID is obviously related to the same reporting entity while remaining unique to its party.

For a single-owner LLC this almost never comes up — one owner, one reference ID, one Form 5472. But if your structure is more complex, the /do-i-need-to-file/ qualifier and the line-by-line /form-5472-instructions/ walk through which parties count as reportable.

Sometimes a foreign owner eventually obtains a US taxpayer identification number — an ITINbecause they took on a personal US filing obligation, or an EIN for another US venture. When that happens, the owner now has a real US-issued number that can identify them on Form 5472, and you may begin using it instead of the made-up reference ID.

Handle the transition cleanly

The cleanest approach is to switch to the real TIN starting with the first filing year for which the owner held it, and to keep a note in your records linking the old reference ID to the new US number. Do not go back and amend prior years just to swap the identifier — those years were correct when filed, and the reference ID did its job. Consistency still matters: once you adopt the real TIN, use it every year going forward rather than alternating between it and the old reference ID.

A disregarded foreign-owned LLC files Form 5472 attached to a pro forma Form 1120— the 1120 acts as a cover page so the 5472 has something to attach to. People sometimes assume the reference ID belongs on the 1120 too, but it does not. The 1120 is the LLC’s form, so it shows the LLC’s EIN at the top. The reference ID lives on Form 5472, where it identifies the related party.

Filing method matters too

Because the entity is disregarded, this package cannot be e-filed. You mail it to P.O. Box 149342, Austin, TX 78714-9342 or fax it to 855-887-7737. Getting the identifiers, the attachment order, and the filing method all correct is exactly the kind of detail covered in /how-to-file-form-5472/ and shown on the /form-5472-example/ page.

Because the reference ID is something you create rather than something the IRS mails you, there is no official record of it anywhere except your own files. That makes a small private ledger essential. Next year’s filing has to reproduce the exact same string, and the year after that, indefinitely — so the safest place to store it is alongside the LLC’s permanent records with the EIN letter and formation documents.

What the ledger should contain

It does not need to be elaborate. A single small table is plenty: the related party’s name, the reference ID you assigned, the date you first used it, and the years it has appeared on a filed Form 5472. Storing the years filed alongside the ID also doubles as a compliance checklist — you can see at a glance whether any year was missed.

Keep this with the records that support the Form 5472 itself, since §6038A also requires the LLC to maintain records substantiating the reportable transactions. If you hand the filing to us, we keep the assigned reference ID on file so each year’s filing reuses it exactly.

Catch-up filers — founders who learn about Form 5472 after one or more years have already passed — ask whether each late year needs its own identifier. It does not. The reference ID identifies the party, not the year. So if you are filing 2023, 2024, and 2025 all at once, the foreign owner should carry the same reference ID, for example 98-7654321-001, on every one of those forms. Switching the ID between back years would recreate exactly the matching confusion the reference ID exists to prevent.

The penalty stacks per form, per year, with no cap and no statute of limitations, so three unfiled years is up to $75,000 of exposure. That is why prompt catch-up filing matters — and why consistency across those back years is part of doing it correctly. The /form-5472-catch-up-filing/ page covers the late-filing process; this flat $299service handles the identifiers and the paperwork for each year.

None of these mistakes are exotic, which is what makes them common. They come from the fact that the reference ID is self-assigned and lightly regulated, so filers improvise without realizing the few firm rules. The good news is that every one of them is easy to avoid once you know it exists.

An incomplete Form 5472 is treated the same as an unfiled one for penalty purposes, so a missing or malformed reference ID is not a harmless typo. When in doubt, use the EIN-plus-sequence convention, write it down, and reuse it. To see a correctly completed identifier in context, the /form-5472-example/ and /what-is-form-5472/ pages show where it sits on the form.