The reference number on the W-8BEN is an optional entry on Line 7 that either you or your withholding agent can use to tie the form to a specific account or internal record. It is not issued by the IRS, it is not a tax identification number, and leaving it blank does not invalidate the form. If your bank or broker asked you to write a specific number there, use that number. If no one asked, leave it empty.
What Line 7 Is For
Line 7 exists so the withholding agent — the bank, brokerage, or other payer of U.S. source income — can match your W-8BEN to the right account in their system. The IRS instructions describe it as a line that “may be used by the filer of Form W-8BEN or by the withholding agent to whom it is provided to include any referencing information that is useful to the withholding agent in carrying out its obligations.”1Internal Revenue Service. Instructions for Form W-8BEN (Rev. October 2021)
In practice, that usually means a customer account number or an internal code the payer uses on their end. A withholding agent who needs to link your W-8BEN to a Form W-8IMY (used for intermediaries and flow-through entities) may also ask you to enter a specific code on Line 7 so the association between the two forms is clear.1Internal Revenue Service. Instructions for Form W-8BEN (Rev. October 2021) Either way, it is a recordkeeping field, not part of your certification of foreign status.
What to Put on Line 7
If your withholding agent gave you a specific number — an account number, a client ID, or an internal reference code — enter exactly that. Don’t invent a number and don’t reuse a tax ID from elsewhere on the form. The field belongs to the payer, so the payer decides what belongs in it.
If you were not given anything, ask before guessing. Many withholding agents handle the matching internally and never need the filer to put anything on Line 7 at all.
When Line 7 Actually Matters
You Own a Disregarded Entity
If you are a foreign individual who owns a disregarded entity, such as a single-member LLC treated as nonexistent for tax purposes, you fill out the W-8BEN in your own name. But the account receiving payment may be held in the entity’s name. The IRS instructions say you should include the disregarded entity’s name and account number on Line 7 so the withholding agent can connect your certification to the correct payment stream.1Internal Revenue Service. Instructions for Form W-8BEN (Rev. October 2021)
You Hold Multiple Accounts With the Same Payer
If you have more than one account with the same withholding agent, Line 7 tells the payer which account this particular W-8BEN covers. You can list the account number the form is for.1Internal Revenue Service. Instructions for Form W-8BEN (Rev. October 2021) Some withholding agents will ask you to submit a separate W-8BEN for each account, each carrying its own reference number.
When to Leave Line 7 Blank
If no one asked you for a reference number, leave the line empty. Line 7 has no bearing on your certification of foreign status or your eligibility to claim treaty benefits, and a blank Line 7 does not make the form invalid.1Internal Revenue Service. Instructions for Form W-8BEN (Rev. October 2021) The certification is carried by the identification, address, treaty claim, and signature sections, not by Line 7.
Don’t Confuse Line 7 With the Tax ID Fields
The W-8BEN has several identification fields, and treating the reference number as your tax ID (or the other way around) is a common mistake that can hold up processing or trigger full 30% withholding. Line 7 is not a substitute for any of the tax number fields.
- Line 5 asks for your U.S. Taxpayer Identification Number — your SSN or ITIN. You generally need this to claim a reduced rate under a tax treaty.
- Line 6a asks for your Foreign Tax Identifying Number, meaning the tax ID issued by your country of residence. If you hold a financial account at a U.S. institution and receive reportable U.S. source income, you generally must provide your FTIN, unless your country does not issue them or you are not legally required to obtain one, in which case you check the box on Line 6b.1Internal Revenue Service. Instructions for Form W-8BEN (Rev. October 2021)
- Line 7 is the reference number. Optional, not a tax ID, and used only for the payer’s internal tracking.
If Line 6a is required in your situation and you skip it because you assumed Line 7 covered your identification, the withholding agent may treat the form as invalid. The reference number never fills that role.