Turning 18 in high school: contracts, parental authority, voting, and what stays at 20
18歳で成年に（契約・親権・選挙権と20歳のまま変わらないこと）
- Applies to
- All of Japan
- Source last checked
- , Open the Japanese source
- Official source
- 民法（成年年齢関係）改正 Q&A（法務省）
Since 1 April 2022, a person in Japan becomes a legal adult, 成年 (seinen), at 18 instead of 20. Japan's school year groups children born from 2 April to 1 April, so nearly every student turns 18 during the third year of high school, 高3 (kō-san). Some are adults in April; others only at the very end of the year. Here is what changes on that birthday and what does not.
What "adult" means in the Civil Code
The Ministry of Justice explains that the age of adulthood in the Civil Code, 民法 (minpō), carries two meanings: the age at which a person can sign a contract alone, and the age at which they stop being under parental authority, 親権 (shinken):
単独で契約を締結することができる年齢という意味と、親権に服することがなくなる年齢という意味
The ministry's reason for the change: voting and the constitutional referendum had already moved to 18, most countries set adulthood at 18, and treating 18- and 19-year-olds as adults respects their right to make their own decisions.
Anyone born on or after 2 April 2004 becomes an adult on their 18th birthday.
What changes at 18, and what stays at 20
| Item | Age | What the ministries say |
|---|---|---|
| Sign a contract without a parent's consent (phone, flat, credit card, car loan) | 18 | A loan can still be refused if it is beyond the person's ability to repay |
| Decide where to live, and whether to study or work | 18 | Parental authority ends; the ministry adds that the understanding of parents and teachers still matters |
| 10-year passport | 18 | |
| Work in a licensed profession such as certified accountant (公認会計士) or judicial scrivener (司法書士) | 18 | After passing the exam |
| Apply to change legal gender status (性別の取扱いの変更審判) | 18 | |
| Marry | 18 for everyone | The age for women was 16 before April 2022 |
| Vote (Japanese nationals) | 18 | Since 2016, under the election law |
| Drink alcohol, smoke | 20 | Unchanged, for health reasons |
| Bet on horse, bicycle, motorcycle or motorboat races (公営競技, kōei kyōgi) | 20 | Unchanged, to prevent gambling addiction |
The alcohol and tobacco line, in the ministry's words:
お酒やたばこに関する年齢制限については，２０歳のまま維持されます。
The right to cancel a contract ends at 18
This is the change that matters most in 高3. Under 18, a minor who signs a contract without a parent's consent has the 未成年者取消権 (miseinensha torikeshi-ken, the minor's right to cancel): the minor or the parent can cancel the contract as if it had never been made. The ministry's youth site explains that from adulthood a person can sign alone, and can no longer cancel afterwards.
The ministry names this directly as a concern: 18- and 19-year-olds can no longer use the right to cancel, and consumer harm from bad sales practices may grow. Its answer is consumer education and changes to consumer-contract law. At home, the practical answer is a conversation before the birthday.
Voting at 18
Voting moved to 18 under a separate law, the Public Offices Election Act. The Ministry of Internal Affairs sets the conditions:
| Election | Who can vote |
|---|---|
| National (House of Representatives, House of Councillors) | 日本国民で満18歳以上であること |
| Prefectural (governor, assembly) | Japanese national, 18 or over, living in the same municipality in that prefecture for 3 months or more |
| Municipal (mayor, assembly) | Japanese national, 18 or over, living in that municipality for 3 months or more |
A person counts as 18 from 0:00 on the day before their 18th birthday. The condition is Japanese nationality: a student with only a foreign nationality does not vote in Japanese elections.
Child support agreements
For separated families: if an agreement says support is paid "until the child reaches adulthood" and was made when adulthood was 20, the ministry considers that payment continues until 20. Support also does not end automatically at 18 if the child is not yet financially independent, and the ministry notes it often runs until university graduation. For new agreements it recommends a clear end date, for example "until the March after the child turns 22".
The coming-of-age ceremony
The ceremony, 成人式 (seijin-shiki), is not set by law; each city or town decides. When the ministry wrote its Q&A, most held it around Coming of Age Day in January for 20-year-olds, and it noted the problem of a ceremony in January of 高3, in exam season. Check your own city's notice.
What goes wrong
- A subscription, a loan or any contract signed on a phone after the 18th birthday cannot be cancelled with the minor's right any more.
- Families assume everything moved to 18. Alcohol, tobacco and betting did not.
- A support agreement written as "until adulthood" is read with the age that applied when it was signed.
What to do now
- In 高1 and 高2: talk about contracts, credit cards and online purchases while the right to cancel still protects your child.
- Before the 18th birthday in 高3: agree what your child will check with you before signing anything, and whose name is on the phone contract.
- If your child is a Japanese national, mark the first election after their birthday; the day before the birthday already counts.
- If you pay or receive child support, read the end date in the agreement.
- In January of 高3, look for your city's 成人式 notice to see which age it invites.
Your child's dates, not the general ones
Add your child and ward. The timeline does the rest.