The Tax ID Field: What It Is For, and What If You Have None

The field is not asking whether you owe tax, and it is not asking what you made trading. It is asking something administrative: which tax authority your account details get reported to.

Automatic exchange of financial account information works like this. You open an account with an institution in one place; the institution reports account data to the tax authority there, based on the tax residence you declared; that authority exchanges it with the jurisdictions where you are resident. For any of that to happen, the institution has to establish two facts first — where you are tax resident, and what your number is there. Those are the two boxes on the form.

Which makes it a different question from “do I owe tax on this”. That one is answered by the tax law of your jurisdiction, and it is not what this article is about.

What a TIN is, and “functional equivalents”

The term has a formal definition in the reference form the OECD publishes. That document describes itself as an example rather than a mandatory form — each financial institution is free to use its own — but the elements it collects are the ones the standard requires. It defines the term this way:

The term “TIN” means Taxpayer Identification Number or a functional equivalent in the absence of a TIN. A TIN is a unique combination of letters or numbers assigned by a jurisdiction to an individual or an Entity and used to identify the individual or Entity for the purposes of administering the tax laws of such jurisdiction.

The appendix adds the part that resolves most of the confusion:

Some jurisdictions do not issue a TIN. However, these jurisdictions often utilise some other high integrity number with an equivalent level of identification (a “functional equivalent”). Examples of that type of number include, for individuals, a social security/insurance number, citizen/personal identification/service code/number, and resident registration number.

So not holding a card that says “taxpayer identification number” does not mean you have no TIN. In plenty of jurisdictions the number simply lives on a different document.

Where to find your number

The answer is jurisdiction-specific and it is published, so this is one of the few form fields you should never have to guess at.

The OECD maintains reference material on acceptable TINs by jurisdiction, and several national tax authorities republish it in their own language. China's State Taxation Administration, for example, hosts a TIN rules lookup compiled from the OECD's information; on the day we read it the page covered 118 countries and territories and stated that it was compiled from what the OECD page showed on 21 April 2026, listing number lengths, the documents that carry them and their formats for individuals and entities.

Two things worth holding on to before you look yours up:

• The number can sit on completely different documents in different places. Somewhere it is a dedicated tax reference; somewhere else it is the national ID number; elsewhere a social security number. Reasoning by analogy from a neighbouring country is how people get this wrong.
• Dual residence is possible. The form has room for more than one jurisdiction for a reason. The self-certification's own definitions note that dual resident individuals may rely on tie-breaker rules in tax conventions to resolve which jurisdiction they are resident in — which is a question for a tax adviser, not for a verification flow.

When there really is none: three reasons

This is the part almost nobody covers, and it is printed on the OECD form itself.

Above the table where you enter the number, the form says that if a TIN is unavailable you should provide the appropriate reason A, B or C. Verbatim:

The three are not interchangeable, and C is the one most often picked wrongly — its condition is that the jurisdiction's own law does not require collection, not that you would rather not supply it.

What you are meant to do is pick the one that is true and say so. Entering a number that does not exist and writing “I cannot obtain one, because…” are not two versions of the same shortcut. On a signed declaration they are different acts.

Why trading platforms started asking

These boxes used to belong to bank and broker onboarding. They arrived at crypto platforms because a reporting framework aimed specifically at crypto-assets came into effect.

The OECD Global Forum publishes the list of jurisdictions that have committed to it. The version we read is marked “Last update: 23 June 2026” and sorts them by the year of first exchange:

• First exchanges by 2027 — 46 jurisdictions, including Austria, Belgium, Brazil, the Cayman Islands, Chile, Croatia, Denmark, France, Germany, Indonesia, Ireland, Italy, Japan, Kazakhstan, Korea, Luxembourg, the Netherlands, New Zealand, Norway, Poland, Portugal, South Africa, Spain, Sweden, Uganda and the United Kingdom.
• First exchanges by 2028 — 29 jurisdictions, including Australia, the Bahamas, Bahrain, Barbados, Bermuda, the British Virgin Islands, Canada, Gibraltar, Hong Kong (China), Israel, Kenya, Malaysia, Mauritius, Mexico, Nigeria, Panama, the Philippines, Singapore, Switzerland, Thailand, Türkiye and the United Arab Emirates.
• First exchanges by 2029 — 1 jurisdiction: the United States.

The same document lists five jurisdictions identified as relevant to the framework that had not yet committed: Argentina, El Salvador, Georgia, India and Viet Nam. We are reporting what that file lists and drawing no inference about anywhere it does not mention.

For an individual the schedule means one thing: which group your jurisdiction falls into is roughly what determines when these fields reach you. It has nothing to do with whether you have made money.

When the question actually appears

A common assumption is that only US persons get asked about tax status. The field order in a real flow says otherwise.

Take the onboarding update Binance published for users moving to its locally licensed UAE entity. The help page lists the steps, and the tax-related ones come near the end:

1. Declare whether you are a US citizen, a green card holder or a US tax resident.
2. Declare whether you hold citizenship in a country other than the nationality on the ID you submitted earlier.
3. If you hold multiple citizenships, specify your tax residency country and provide your Tax Identification Number(s).
4. Declare your obligation to notify the entity of any change in tax residency, and acknowledge your commitment to comply with the applicable information-exchange requirements.

Two things stand out. The trigger is multiple citizenship, not being American. And the last step is a continuing obligation — after a move, a change of residence status or a second passport, your address is not the only thing that needs updating.

Every platform and jurisdiction words this differently; the above is one verifiable example, not a prediction of the screens you will see. If you want the address half of the same form sorted first, see what a proof of address actually proves; if the country field itself is the problem, see country and residence: choosing it, fixing it.

This is a signed declaration

A self-certification is not an ordinary form field. It is a declaration you put your name to.

HMRC's international exchange of information manual, in its section on penalties for failure to provide a valid self-certification, states that an account holder asked for one by a reporting financial institution must provide a valid self-certification in accordance with the CRS and/or FATCA agreement, and that failing to do so attracts a penalty of up to £300 where the failure is deliberate or due to a failure to take reasonable care.

The amount is small; the point is who it lands on. This is a penalty aimed at the person making the declaration, not at the institution — which tells you how the document is treated legally. Elsewhere the same manual explains that an institution has reason to know a self-certification is unreliable where information in its own files conflicts with what you claimed. A number typed in to get past a screen does not simply sit there unexamined.

Penalties differ by jurisdiction; the above is the UK position and does not transfer. It is here to make one point: filling the box carelessly is not the low-effort option, it is a signature.

What this site will not do

A boundary, not boilerplate:

• No tax advice. How to complete this field is an identity-verification question. Whether you owe tax, how much and when to file is a tax question — for your tax authority or a qualified adviser.
• No help choosing a jurisdiction. Tax residence follows from each jurisdiction's law, can apply in two places at once, and where it does the tie-breaker rules in the relevant tax convention decide — a point the self-certification's own definitions make.
• Nothing on arrangements to narrow what gets reported. Searching these terms turns up a steady supply of material marketing a tax number in one jurisdiction or another. We do not cover it.

Questions people actually ask