Your baby may have a US tax number before a British passport

Figures relate to tax year 2025-26 (UK) · 2025 (US)

A baby is born in a London hospital. One parent is American. The midwife says nothing about tax, and why would she.

Yet a child born abroad to an American parent may already be a US citizen. Not eligible to be one. Already one.

So a tax relationship begins at birth. It stays quiet for years, then surfaces at the worst moment.

Key takeaways

• Citizenship can pass at birth, with no paperwork needed.
• A child born abroad still needs it documented to prove it.
• The consular birth report is far easier before the fifth birthday.
• A social security number is the key that unlocks everything else.
• Filing starts only once the child has income of their own.
• A Junior ISA is the usual problem account.
• Credits can be worth claiming even with no tax due.
• Fixing this at 25 costs far more than doing it at one.

What makes a child born abroad American?

Descent, not registration. If a parent is a US citizen and meets a residence test, citizenship passes at birth. Per IRS guidance for citizens abroad, the duty to file follows citizenship rather than where somebody lives. So the status exists whether or not anyone files a form.

Nothing you do creates it.

Paperwork only proves what already happened.

What is the parent residence test?

A rule about how long the American parent lived in the States. Where both parents are American, the test is light. Where only one is, that parent generally needs five years of physical presence, at least two of them after age 14.

Count the years before assuming anything.

Young parents are the ones who fail it.

What if the parent does not meet it?

Then citizenship may not pass at all, and the child is simply British. That outcome surprises families who assumed an American passport was automatic. It is worth checking properly rather than guessing, because the answer shapes everything else.

Grandparents can sometimes help in limited cases.

But the rules there are narrow.

What is a consular report of birth?

The document that records the birth with the American authorities. You apply at the embassy, show the evidence of the parent's residence, and receive a certificate. It then works like a US birth certificate for the rest of the child's life.

Apply before the fifth birthday if you can.

After that the process gets harder.

Why does the fifth birthday matter?

Because the easy route closes. Before five, the consular report is a routine application. Afterwards families often need a different and slower process, with more evidence about the parent's years in the States. Those records get harder to find each year.

Old payslips and school records matter here.

Gather them while they still exist.

Does the child need a social security number?

Yes, and it unlocks everything else. Without one you cannot claim credits, open certain accounts, or file a return for the child later. You can apply alongside the consular report, which saves a second round of appointments.

Our guide to ITIN applications from the UK covers the alternative number.

Do both applications together.

When does the child have to file?

Only once they have income of their own above the threshold. A baby with no income files nothing. A teenager with a Saturday job, bank interest or investment income may cross the line, and the duty is theirs rather than yours.

Pocket money and gifts do not count.

Interest and dividends do.

What counts as the child's income?

Anything held in their name. Bank interest, dividends, trust distributions and part-time earnings all belong to the child. Money you hold for them in your own name is yours instead, which is a cleaner position in several ways.

Whose name is on the account decides it.

That single fact drives most of the answer.

A worked example

Take an illustrative example. A child born in Leeds in 2010 to one American parent receives a Junior ISA from grandparents.

It grows quietly to £28,000 by her eighteenth birthday. Nobody has mentioned America to her.

Because the fund inside it is a foreign pooled investment, the American rules treat it harshly.

So a wrapper that is tax free in Britain produces an American bill and years of back filing at exactly the moment she applies to university.

Two systems, one childhood

Why is a Junior ISA a problem?

Because the wrapper means nothing to the IRS. What matters is the fund inside, and a British fund is a foreign pooled investment under American rules. Those rules apply a punitive regime designed for something else entirely.

Our guide to Junior ISAs and US child tax covers it in detail.

Cash versions avoid the worst of it.

What should grandparents do instead?

Give cash, or hold the investment themselves. A gift of money creates no American problem for the child, while a funded investment account can create one that lasts decades. Many families simply keep the holding in a British relative's name.

Our guide to US gift tax for expats covers the giving side.

Intentions are good, wrappers are not.

Can you claim credits for the child?

Sometimes, and it can be worth real money. The child tax credit may be available where the child has a social security number issued in time. Rules on the refundable part change, so check the current position each year.

Our guide to the child tax credit abroad covers the claim.

No number means no credit at all.

Does the British parent have to do anything?

Nothing for themselves, but plenty as a signatory. A non-American parent operating the child's accounts can be dragged into reporting questions. Keeping the parents' finances separate from the child's keeps that simple.

Our guide to a non-resident alien spouse covers the wider position.

Signatory is not the same as owner.

What about child benefit?

It is a British matter and America ignores it. What does matter is the high income charge that can claw it back from a higher earning household. That is a UK question, though it often lands on the same family.

Our guide to the high income child benefit charge covers it.

Claim it anyway to protect the record.

What happens at sixteen?

Britain issues a National Insurance number and the child starts work. Earnings from a first job are usually small enough to fall under the American threshold, but not always. A well paid gap year can tip them over.

Check the threshold for that year.

It moves with inflation each year.

What happens at eighteen?

The accounts become theirs. A Junior ISA matures, savings transfer into their name, and whatever sat quietly for years is suddenly their own income. This is when most families discover the problem for the first time.

Plan the eighteenth birthday in advance.

Waiting until it happens is the expensive route.

What if nobody registered the birth?

The child is still a citizen if the test was met. Registration proves the status rather than granting it, so a gap in paperwork does not remove the duties. Many young adults discover this when applying for a first passport.

Our guide to the accidental American covers that discovery.

In our practice this is the commonest route in.

Can a young adult catch up?

Usually, and far more easily than they fear. The streamlined route exists for people who did not know they had to file. A student with modest income often ends up owing nothing at all once the returns are prepared.

Our streamlined filing service handles the catch-up.

Fear of the bill is usually worse than the bill.

Can the child give up citizenship?

Not as a child, because the decision has to be their own. A minor cannot renounce in any reliable way, so the question waits until adulthood. By then there may be years of filings to tidy up first.

Our guide to renouncing US citizenship covers the exit.

You must be compliant before you can leave.

What about a child born to two Americans?

The test is lighter and the outcome more certain. Where both parents are citizens, only one needs to have lived in the States at some point. Most such children are citizens without any difficulty at all.

Registration is still worth doing early.

Proof matters when passports are applied for.

What about adoption?

Different rules apply and they are more involved. An adopted child does not automatically acquire citizenship by descent in the same way, and timing and residence conditions matter. Families in that position should take advice before assuming the position.

The route depends on the adoption order.

Do not reason by analogy here.

Does the child need to report accounts?

If the balances cross the thresholds, yes. A child with accounts over the reporting limits has the same duties as an adult, though a parent signs for them. Junior accounts count towards those totals.

Our guide to the FBAR covers the thresholds.

Totals are aggregated, not per account.

What records should parents keep?

The consular report, the social security card, and proof of the parent's years in the States. Add statements for any account in the child's name. Those four things answer nearly every question that arrives later.

Keep them somewhere the child can find them.

They will need them long after you have moved house.

Does it affect your will?

It can, because an American child inherits American reporting with any trust interest. A legacy routed through a British trust may hand a young adult annual filings nobody intended. So the drafting deserves a second look.

Our guide to wills for Americans in the UK covers the drafting.

Name the problem before the solicitor drafts.

What about a child born in America to British parents?

That runs the other way, and the result is the same. A baby born on American soil is a citizen by birth, whatever passports the parents hold. Families who were there briefly for work often bring a US citizen home without realising it.

A short posting can have long consequences.

The hospital paperwork is the only clue most parents get.

Does the child need a British passport as well?

Usually yes, and holding both is perfectly normal. Britain and America both accept dual nationality, so a child born abroad can carry two passports for life. Americans are expected to enter and leave the States on the American one.

Travel is simpler with both in date.

Renewal dates rarely line up, so diarise them.

What if the parents separate?

The child's status does not change, but the practicalities do. Whoever holds the documents controls how easily anything gets done, and a consular application generally wants both parents to consent. Agreeing that early avoids a stuck application years later.

Keep copies with each parent.

Originals go missing exactly when they are needed.

Does university funding change anything?

It can, in both directions. British student finance is unaffected by American citizenship, so nothing is lost there. Some American savings vehicles are useful if the family plans a US university, though they bring their own reporting while the child lives here.

Decide which country the degree will be in.

That answer drives the sensible wrapper.

What if the child moves to America later?

Then the filing history matters a great deal. A young adult arriving to work or study will be asked for a number and a record, and gaps surface immediately. Sorting the position before the move is far easier than during it.

Employers ask for the number on day one.

So the catch-up belongs before the flight, not after.

Does the child need to worry about a British pension?

Not for many years, but the groundwork starts early. A child born abroad who later works here will build National Insurance credits, and a workplace pension will follow automatically from the first proper job. Those pensions are generally well treated under the treaty, so they are rarely the problem. The trouble sits with ordinary investment accounts opened with good intentions long before.

Pensions are the one wrapper that travels well.

So a workplace scheme is not something to avoid.

What does this cost a family to put right?

Far less early than late, and the gap is large. Registering a birth and obtaining a number is a modest administrative exercise in the first year. Leaving it until a young adult has matured accounts, a part-time income and a university application running costs several years of back filings instead, plus the investment problem nobody priced at the time.

In our practice the late cases take months, not weeks.

Early paperwork is the cheapest tax planning there is.

How to register a child born abroad

1. Check whether the American parent meets the physical presence test.
2. Gather proof of those years before the records disappear.
3. Book the consular appointment well before the fifth birthday.
4. Apply for the social security number at the same appointment.
5. Keep the certificate and card together, permanently.
6. Hold gifts as cash rather than funded investment accounts.
7. Review the position again when the child turns sixteen.
8. Plan the eighteenth birthday before the accounts mature.

Mistakes and penalties we see with a child born abroad

The first is assuming no passport means no citizenship, which gets the position exactly backwards.

The second is a well meant Junior ISA that creates a decade of American problems.

The third is missing the fifth birthday and facing a far harder registration.

The fourth is leaving everything until the child is eighteen and applying to university.

How US UK Tax Accountants helps

We check first whether citizenship actually passed, because families often assume wrongly in both directions. That answer decides whether anything else matters.

Then we set up the accounts so nothing nasty matures at eighteen. We also tidy up young adults who find out late.

If you have a child here with an American parent, get in touch while the paperwork is still easy.

Last reviewed 21 October 2026. This article is general information and not personal tax advice, and citizenship rules change over time.

For the neighbouring question, Six months to decide something they have never heard of walks through it in detail.