US–Japan Dual Citizenship for Your Children

If one parent is American and the other Japanese, your child is almost certainly born with both nationalities. The two countries then treat that very differently — the US shrugs, Japan officially asks you to choose — and there are a couple of traps that can cost the child a citizenship if you miss them. This guide maps both sides. (For the birth and citizenship paperwork itself, start with Having a Baby in Japan.)

Born with both

Japan grants nationality by descent, not birthplace: a child is Japanese at birth if either parent is a Japanese national (Nationality Act, Art. 2) — no matter where the child is born. The US side independently makes the child a US citizen (by birth on US soil, or by descent if born abroad and the transmission rule is met). Put together, the typical US–Japan child is dual from the first day.

The US side: no need to choose

This part is easy. US law does not require a citizen to choose between US and any other nationality — “U.S. law does not require a U.S. citizen to choose between U.S. citizenship and another (foreign) nationality.” Your child keeps US citizenship for life regardless of what Japan’s rules say, because only the citizen’s own deliberate act can give it up (more on that below).

The one rule to remember is at the border: a US citizen, including a dual one, enters and leaves the US on the US passport, and uses the Japanese passport for Japan. Carry both, and hand over the right one at each end.

Japan’s nationality-selection rule — and how it actually plays out

On paper, Japan expects a dual national to pick one nationality. Under the nationality-selection rule (国籍選択kokuseki sentaku, Art. 14) — with the ages as they stand since the 2022 adulthood reform:

• If the child became dual before age 18 (which is the case for anyone dual at birth), they must choose by the time they turn 20.
• If someone becomes dual at or after 18, they choose within two years.

(Note the deadline age is 20, not 18 — lowering adulthood to 18 didn’t move it.)

How you “choose” Japanese. The usual route is a declaration of choice filed at city hall (or a consulate abroad): you declare that you choose Japanese nationality and will give up the other. Importantly, that filing doesn’t require any proof that you actually renounced the US citizenship — and the law’s accompanying duty to “endeavor to renounce” the foreign nationality (Art. 16) is an effort obligation with no penalty attached.

What actually happens in practice. This is where the gap between the rule and reality matters. The only way Japan can strip nationality for not choosing is for the Minister of Justice to issue a formal written demand to choose; miss that by a month and you lose Japanese nationality. But by the government’s own testimony in the Diet, that demand has never been issued — not once. The practical result is that large numbers of people quietly remain dual.

Two cautions on how to read that:

• It is tolerance, not a right. Japan still officially requires single nationality; the rule is on the books and could be enforced or changed. This is a gray area to navigate with awareness (and, for anything consequential, professional advice) — not a guarantee.
• Don’t confuse it with the rule that is enforced. A separate provision (Art. 11) says a Japanese national who, as an adult, voluntarily naturalizes into another country loses Japanese nationality automatically — and that one genuinely bites (tens of thousands have lost it that way). Being dual from birth is not that; your child only triggers it if they later go out and actively acquire a third nationality by application.

The trap: a baby born outside Japan (国籍留保)

If your child is born outside Japan — in the US, say — and picks up that country’s citizenship by birth, there’s a hard deadline that catches families every year. The Japanese parent must file a reservation of Japanese nationality (国籍留保kokuseki ryūho) together with the birth notification, within three months of the birth. Miss it, and the child loses Japanese nationality retroactively to birth — treated as if they were never Japanese.

It’s not a separate errand: the overseas birth registration (出生届shusshō todoke) form has a 国籍留保kokuseki ryūho box the parent signs. The fix if it’s missed is narrow — the child can later reacquire Japanese nationality by notification, but only while under 18 and living in Japan (otherwise it’s full naturalization). So for a Japanese parent giving birth back in the States, this three-month window is the thing not to let slide. (A baby born in Japan doesn’t face this — see Having a Baby in Japan.)

If they ever do give up US citizenship — the exit-tax angle

Some dual kids, as adults, decide to keep only their Japanese nationality. Two things to know:

• A minor can’t simply renounce US citizenship — and a parent cannot do it for them. A child under 16 is presumed too young; under 18 there are extra safeguards; and a renunciation before 18 can even be undone within six months of turning 18. So this is realistically a young-adult decision, made deliberately.
• The exit tax has a built-in break for people dual at birth. Normally, giving up US citizenship runs you through the “covered expatriate” tests (net worth ≥ $2 million, a high recent tax bill, or failing to certify tax compliance) and a possible mark-to-market exit tax. But there’s an exception precisely for someone who was a dual citizen at birth — still a citizen of, and taxed as a resident of, the other country, and not a long-term US resident — which spares them the net-worth and income tests. The catch: it only works if they’ve filed and certified five years of US tax compliance. (A separate exception covers those who expatriate before about 18½.)

The throughline: keep the child US-tax-compliant from the start. It’s a minor chore while they’re young, and it’s the very thing that later keeps a clean exit available if they choose one.

Don’t forget: a dual kid is a US taxpayer too

US citizenship comes with US tax obligations at any age — worldwide income, and an FBAR once their foreign accounts cross $10,000 (an account a grandparent opens in the child’s name counts). It rarely means tax owed while they’re small, but the filing thread is real and it’s what preserves the options above. The details are in Your Dual-Citizen Child’s US Taxes.

The short version

• A US–Japan child is usually born dual (Japan by descent from either parent; the US by birth or transmission).
• The US never makes you choose — your child keeps US citizenship for life; just use the US passport for the US, the Japanese one for Japan.
• Japan’s selection rule says choose one (for a child, by age 20), but the power to strip nationality over it has never been used — many stay dual in practice. Treat it as tolerated, not guaranteed.
• Different rule, actually enforced: voluntarily naturalizing into another country as an adult loses Japanese nationality.
• Born abroad? File 国籍留保kokuseki ryūho within 3 months of the birth (on the 出生届shusshō todoke) or the child loses Japanese nationality.
• If they ever give up US citizenship, the dual-citizen-at-birth exit-tax exception can spare them the worst of it — but only if they’re tax-compliant, so keep them filing.

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This guide is general information, not legal or tax advice. Nationality and expatriation rules are intricate, change over time, and turn on individual facts — verify against the sources below and consult a nationality lawyer and a cross-border tax professional before making any decision about a child’s citizenship.