A My Number notice arrived: what to do with it

If a registered letter marked 個人番号通知書 (kojin bangō tsūchisho — individual number notice) arrived a few weeks after you registered your address, open it and keep it somewhere safe. It tells you your My Number. You don't need to do anything else with it today.

What the notice is

Everyone with a resident record in Japan gets a 12-digit number, and that includes foreign nationals once the ward has registered them. The Digital Agency says the number is used for social security, tax and disaster-response procedures.

The notice is posted by registered mail. J-LIS, the body that issues the cards, says it goes out about two to three weeks after the ward registers you.

The number is yours for life. It doesn't change when you move within Japan. If you leave Japan and later come back to live here, you get the same number again.

What the notice is not

The paper is not an identity document. J-LIS says it cannot be used to prove your number or your identity, and it cannot be reissued if you lose it.

When an office needs proof of the number, you show either a My Number card or a copy of your resident record (住民票の写し, jūminhyō no utsushi) with the number printed on it. You can ask for that copy at the ward office. So losing the notice is a nuisance, not a crisis.

If you missed the delivery

Registered mail needs a signature at the door. If nobody is home, the post office leaves a slip. If the letter is never collected or redelivered, it goes back to the ward. The envelope is also marked “do not forward”, so a postal forwarding order won't catch it.

Wards differ in how long they keep a returned letter. Shinjuku keeps it until the end of the sixth month after it came back. You collect it at the main office counter with photo identification. If you live elsewhere, ask your ward's resident registration desk.

Who may ask for the number

Your employer will ask for the number for tax and social insurance paperwork. A bank may ask for it when you open certain accounts. The Digital Agency's list also names the tax office, the local government, Hello Work, the pension office and health insurers.

Outside those procedures, the law limits who is allowed to ask for the number. A landlord or an online shop has no reason to ask for it, so don't give it.

The card is optional

The plastic マイナンバーカード (My Number card) is a separate thing from the notice. Getting one is not compulsory. Applying is free, and the Digital Agency says the card takes about a month.

You can apply online with a photo, by post, or at some photo booths. About a month later a postcard arrives telling you where to collect the card. Bring that postcard and photo identification such as your residence card. You set the PINs at the counter.

What the card does for you

It works as photo identification, and it proves your number at the same time. That saves carrying your passport to a bank or a phone shop.

It lets you print a copy of your resident record and other certificates at a convenience store. The convenience store service usually runs from 6:30 to 23:00 every day, and the certificates on offer depend on your municipality.

It can be your health insurance card. Paper insurance cards stopped being issued on 2 December 2024, and the old ones expired on 1 December 2025. If you don't register a My Number card for insurance, your insurer sends you a 資格確認書 (shikaku kakuninsho — eligibility certificate) without you applying, and you show that instead.

When you move to another city or ward, the card lets you file the moving-out notice online through the government portal. You still go to the new ward office in person to register the new address.

The expiry rule that catches foreign residents

For a foreign resident with a fixed period of stay, the card's expiry date is the last day of that period, not the usual ten years.

Renewing your residence card does not extend the My Number card by itself. Bunkyo ward says you bring the new residence card and the My Number card to the ward counter and ask for the expiry date to be updated. If your new residence card hasn't arrived yet, Bunkyo can extend the My Number card by two months while the application is pending.

Miss that step and the card stops working on its expiry date. The Immigration Services Agency warns that an expired card can no longer be used as identification or for online procedures. You would have to apply for a new card.

So if you get a card, write its expiry date next to your residence card's date.

If you decide against the card, the notice itself is enough for now. Keep it with your passport, and take it out the day your employer's forms ask for the number.