Is it true that there is no penalty if you file an amended return?

“Even if you make a mistake in your final tax return (kakutei shinkoku), if you file an amended return yourself there is no penalty at all.” Have you heard this before?

It is true that correcting the mistake yourself, and early, makes the burden lighter. But it is not “nothing at all.” If you leave it alone and have to correct it after a tax audit, the burden becomes heavier.

We checked this rumor against the original text of the Act on General Rules for National Taxes and the official information published by the National Tax Agency (NTA).

Four tax terms to know first

• Amended return (shūsei shinkoku) = The procedure in which, when you find that the tax shown on a return you have already filed is too small (this includes cases where the refund was too large), you correct it yourself and report the additional tax.
• Delinquency tax (entai-zei) = Money added to your tax when you pay late, calculated for the number of days you were late. You can think of it as something like interest.
• Additional tax (kasan-zei) = Money added on top of the original tax because of a mistake in a return or a failure to file. The additional taxes related to returns are the additional tax for underreporting, the additional tax for failure to file, and the heavy additional tax.
• Waiver ≠ zero burden = The additional tax for underreporting can be waived under certain conditions, but delinquency tax normally applies even to a voluntary correction.

Conclusion

Our verdict: “False.” If you correct the mistake yourself early, the additional tax for underreporting may be waived. But delinquency tax normally remains, and as a rule the burden grows the later you correct it.

Amended return and claim for reassessment

First, let us sort out the names of the procedures. This article covers the case where you notice a mistake after the deadline for the final tax return (the statutory filing deadline) has passed. According to the NTA, there are two ways to correct it.

法定申告期限後に計算違いなど、申告内容の間違いに気が付いた場合は、次の方法で訂正してください。［8］

Reference translation (unofficial): If, after the statutory filing deadline, you notice a mistake in the contents of your return, such as a calculation error, please correct it by the following methods.

The two methods work in opposite directions. If the tax you paid was too little (including cases where the refund was too large), you file an amended return. If the tax you paid was too much (including cases where the refund was too small), you file a claim for reassessment (kōsei no seikyū)［8］.

The basis for an amended return is Article 19 of the Act on General Rules for National Taxes. Let us look at the text (e-Gov Law Search).

先の納税申告書の提出により納付すべきものとしてこれに記載した税額に不足額があるとき。［1］

Reference translation (unofficial): Where there is a shortfall in the amount of tax stated in the earlier tax return as the amount to be paid.

(Article 19, paragraph 1, item 1 · Excerpt)

In other words, it is the procedure in which, when the tax you reported was too small, you correct it yourself and report the additional tax.

On the other hand, the procedure for getting back tax you overpaid is the claim for reassessment. This one has a time limit. Let us look at the text of Article 23 of the Act on General Rules for National Taxes (e-Gov Law Search).

当該申告書に係る国税の法定申告期限から五年（第二号に掲げる場合のうち法人税に係る場合については、十年）以内に限り⁠［2］

Reference translation (unofficial): Only within five years (ten years in the case of corporation tax among the cases listed in item 2) from the statutory filing deadline of the national tax relating to that return.

For income tax the period is five years. For corporation tax it can be ten years depending on the conditions. A claim made because circumstances changed later has a different time limit.

The NTA’s Tax Answer No.2026 gives the same time limit as follows.

更正の請求ができる期間は、原則として法定申告期限から5年以内です。［8］

Reference translation (unofficial): As a rule, the period during which you can file a claim for reassessment is within five years of the statutory filing deadline.

The subject of this article is the amended return, the side where additional tax arises.

Delinquency tax normally applies

When people hear “no penalty,” the thing they most easily overlook is delinquency tax. Its basis is Article 60 of the Act on General Rules for National Taxes. Let us look at the text (e-Gov Law Search).

納税者は、次の各号のいずれかに該当するときは、延滞税を納付しなければならない。［3］

Reference translation (unofficial): A taxpayer must pay delinquency tax when any of the following items applies.

(Article 60, paragraph 1 · Excerpt)

The item that applies to an amended return is this one.

期限後申告書若しくは修正申告書を提出し、又は更正若しくは第二十五条（決定）の規定による決定を受けた場合において、第三十五条第二項（申告納税方式による国税等の納付）の規定により納付すべき国税があるとき。［3］

Reference translation (unofficial): Where a person has filed a late return or an amended return, or has received a reassessment or a determination under Article 25 (determination), and there is national tax to be paid under Article 35, paragraph 2 (payment of national taxes, etc. under the self-assessment system).

(Article 60, paragraph 1, item 2)

This is a little stiff, so here is what it means. When you file an amended return and tax becomes payable, you must pay delinquency tax. The same applies when you noticed the mistake and corrected it yourself. The NTA’s Tax Answer No.9205 explains it as well.

いずれの場合も、法定納期限の翌日から納付する日までの日数に応じた延滞税を納付しなければなりません。［9］

Reference translation (unofficial): In every case, you must pay delinquency tax according to the number of days from the day after the statutory payment deadline to the day you pay.

Delinquency tax is calculated according to the number of days from the day after the statutory payment deadline (the original due date) to the day you actually pay. As a rule, the later you correct, the more delinquency tax there is. (There is a special rule that removes part of the calculation period in some cases, for example when you filed a return on time and then file an amended return after more than one year has passed since the statutory filing deadline［9］.)

The payment deadline for the new tax due under an amended return is the day you file the amended return. Tax Answer No.2026 says so.

新たに納める税金は、修正申告書を提出する日が納期限となりますので、その日に納めてください。［8］

Reference translation (unofficial): The payment deadline for the new tax is the day you file the amended return, so please pay it on that day.

The delinquency tax rate is set each year. The rate for the period in Reiwa 8 (2026) is as follows. For the rates in other years, see the NTA’s Tax Answer No.9205.

令和8年1月1日から令和8年12月31日までの期間は、年2.8パーセント［9］

Reference translation (unofficial): For the period from January 1, 2026 (Reiwa 8) to December 31, 2026 (Reiwa 8), 2.8 percent per year.

(Rate · Excerpt)

If you do not pay within two months after the day following the day you file the amended return, the rate becomes 9.1% per year［9］.

Delinquency tax applies only to the original tax (the principal tax), not to additional tax［9］. Each day the principal tax is paid late adds one more day of delinquency tax. However, if the total delinquency tax is less than ¥1,000, the whole amount is rounded down to zero (Act on General Rules for National Taxes, Article 119, paragraph 4)［7］.

Additional tax changes with timing

Next is the additional tax for underreporting. The standard rate is written in Article 65, paragraph 1 of the Act on General Rules for National Taxes. This is the text of the law itself (e-Gov Law Search).

納付すべき税額に百分の十の割合（修正申告書の提出が、その申告に係る国税についての調査があつたことにより当該国税について更正があるべきことを予知してされたものでないときは、百分の五の割合）を乗じて計算した金額に相当する過少申告加算税を課する。［4］

Reference translation (unofficial): Additional tax for underreporting is imposed in an amount calculated by multiplying the amount of tax to be paid by a rate of 10 percent (5 percent where the amended return was not filed with foresight that a reassessment would be made on that national tax as a result of an audit of the return).

(Article 65, paragraph 1 · Excerpt)

Here is what it means. As a rule, 10% is charged on the new tax you pay. If you file an amended return without foreseeing a reassessment (a tax office action that corrects your tax amount) resulting from a tax audit, the rate is 5%.

There is also a waiver provision, in Article 65, paragraph 6.

第一項の規定は、修正申告書の提出が、その申告に係る国税についての調査があつたことにより当該国税について更正があるべきことを予知してされたものでない場合において、その申告に係る国税についての調査に係る第七十四条の九第一項第四号及び第五号（納税義務者に対する調査の事前通知等）に掲げる事項その他政令で定める事項の通知（次条第六項第二号及び第八項において「調査通知」という。）がある前に行われたものであるときは、適用しない。⁠［4］

Reference translation (unofficial): Paragraph 1 does not apply where the amended return was not filed with foresight that a reassessment would be made on that national tax as a result of an audit of the return, and was filed before the notice of the matters listed in Article 74-9, paragraph 1, items 4 and 5 (advance notice of an audit to the taxpayer, etc.) and other matters specified by Cabinet Order concerning the audit of the return (referred to as the “audit notice” in paragraph 6, item 2, and paragraph 8 of the following Article).

It is long, so here is only the key point. The provision says that no additional tax for underreporting is imposed on an amended return that is filed without foreseeing a reassessment and before the advance notice of an audit arrives. The NTA’s Tax Answer No.2026 confirms this in shorter words.

税務署からの調査の事前通知の前に自主的に修正申告をした場合であれば、過少申告加算税はかかりません。［8］

Reference translation (unofficial): If you voluntarily file an amended return before the tax office’s advance notice of an audit, no additional tax for underreporting is charged.

If you file the amended return after the advance notice, the following applies. The same Tax Answer says so.

税務署からの調査の事前通知の後に修正申告（調査による更正を予知する前の修正申告）をした場合には、新たに納める税金のほかに、新たに納める税金に5パーセントの割合を乗じた過少申告加算税がかかります。［8］

Reference translation (unofficial): If you file an amended return after the tax office’s advance notice of an audit (an amended return filed before foreseeing a reassessment resulting from the audit), in addition to the new tax you pay, additional tax for underreporting of 5 percent of the new tax is charged.

The definition of the advance notice (called the “audit notice” in the text of the law) is given in an NTA pamphlet.

「調査通知」とは、①実地の調査を行う旨、②調査の対象となる税目、③調査の対象となる期間の３項目の通知をいいます。⁠［10］

Reference translation (unofficial): An “audit notice” means a notice of three items: (1) that an on-site audit will be conducted, (2) the tax type subject to the audit, and (3) the period subject to the audit.

In other words, once the tax office sends an advance notice saying “we will conduct an on-site audit, covering this tax type for this period,” you can no longer receive the waiver of the additional tax for underreporting. Separately, no additional tax for underreporting is imposed on the portion for which a “justifiable reason” is recognized for the contents of the return (Article 65, paragraph 5, item 1)［4］. If you file an amended return after the notice but before foreseeing a reassessment, the rate is 5%. An amended return filed after an audit is 10%, as follows.

税務署の調査を受けた後に修正申告（調査による更正を予知した修正申告）をした場合や、税務署から申告納税額の更正を受けた場合には、新たに納める税金のほかに、新たに納める税金に10パーセントの割合を乗じた過少申告加算税がかかります。［8］

Reference translation (unofficial): If you file an amended return after being audited by the tax office (an amended return filed after foreseeing a reassessment resulting from the audit), or if the tax office reassesses your declared tax amount, in addition to the new tax you pay, additional tax for underreporting of 10 percent of the new tax is charged.

To sum up, the additional tax for underreporting is as shown in the table below.

Sources for the table: ［4］［8］

The “portion above the threshold” means the portion that exceeds the larger of the tax amount in the original return and ¥500,000［4］. Even for the same mistake, the rate changes in three steps, 0%, 5% and 10%, depending on when you correct it.

For national taxes whose statutory filing deadline comes on or after January 1, 2024 (Reiwa 6), there are additional surcharge provisions［8］. If you did not present books and records, or if the sales stated were less than one half of the actual amount, 10% of the new tax is added to the additional tax for underreporting. If the stated amount was less than two thirds of the actual amount, 5% is added［8］.

Also, if you did not file a return at all, it is treated differently. The additional tax for failure to file becomes the issue: 15% on the portion of tax up to ¥500,000, 20% on the portion over ¥500,000 up to ¥3,000,000, and 30% on the portion over ¥3,000,000［5］. If you voluntarily file a late return before the tax office’s advance notice of an audit, the rate is 5%［5］.

Worked example: Person A and Person B

Let us calculate the difference in burden for two fictional people. Both left some side-job revenue out of their income tax return for Reiwa 7 (2025), and the additional principal tax each must pay is ¥300,000. The statutory payment deadline for the 2025 income tax was March 16, 2026 (Reiwa 8)［11］.

• Person A = Noticed the mistake in June, filed an amended return on June 15, 2026, before receiving any advance notice of an audit, and paid on that day.
• Person B = Did not notice, received an advance notice of an audit in August, filed an amended return on August 31, 2026, before foreseeing a reassessment, and paid on that day.

Delinquency tax is calculated by multiplying 2.8% per year by the number of days from the day after the statutory payment deadline (March 17) to the payment date. The principal tax is ¥300,000, and for both people the payment date is the day they filed the return.

Person A’s delinquency tax is ¥300,000 × 2.8% × 91 days ÷ 365 days = ¥2,094. Fractions of less than ¥100 are rounded down, so it becomes ¥2,000［7］. For Person B the number of days is 168, so ¥300,000 × 2.8% × 168 days ÷ 365 days = ¥3,866, which becomes ¥3,800 after rounding down the fraction［7］.

Person B’s additional tax for underreporting is ¥300,000 × 5% = ¥15,000. It does not exceed the larger of the tax amount in the original return and ¥500,000, so there is no surcharge［4］.

Adding the ¥300,000 principal tax, the total burden is about ¥302,000 for Person A and about ¥318,800 for Person B. Even for the same ¥300,000 mistake, the timing of the correction makes a difference of about ¥17,000.

• If you do not pay within two months after the day following the filing date, the rate for the later period becomes 9.1% per year, and both people’s delinquency tax increases［9］. The calculation here is a simple estimate that assumes full payment on the filing date.

Concealment and disguising: heavy additional tax

Separate from calculation errors and misunderstandings, there are malicious cases: hiding or falsifying facts, such as leaving out sales or claiming fictitious expenses. These are subject to the heavy additional tax. This is Article 68, paragraph 1 of the Act on General Rules for National Taxes (e-Gov Law Search).

納税者がその国税の課税標準等又は税額等の計算の基礎となるべき事実の全部又は一部を隠蔽し、又は仮装し［6］

Reference translation (unofficial): Where a taxpayer conceals or disguises all or part of the facts that form the basis for calculating the tax base, etc. or the tax amount, etc. of that national tax

(Article 68, paragraph 1 · Excerpt)

The amount imposed in this case is as follows.

当該基礎となるべき税額に百分の三十五の割合を乗じて計算した金額に相当する重加算税を課する。［6］

Reference translation (unofficial): Heavy additional tax is imposed in an amount calculated by multiplying the amount of tax that forms that basis by a rate of 35 percent.

(Article 68, paragraph 1 · Excerpt)

It is 35%, in place of the additional tax for underreporting. It is charged on the part of the tax corresponding to the facts that were hidden or falsified. If you did not file a return at all and also hid facts, it is 40% in place of the additional tax for failure to file［6］. Furthermore, if within the past five years there was a heavy additional tax for the same tax type, or an additional tax for failure to file imposed after foreseeing a reassessment or determination through an audit, 10% is added［6］. So 35% becomes 45%, and 40% becomes 50%.

Under the text of the law, an amended return filed voluntarily without foreseeing a reassessment is excluded from the heavy additional tax［6］. An amended return filed after you learn that an audit has begun is, as a rule, treated as filed after foreseeing a reassessment, and the 35% is not reduced［12］.

What to do

Here are the steps that keep your burden to a minimum when you notice a mistake.

The NTA also calls on taxpayers to file an amended return as soon as possible once they find an error［8］.

Summary

“No penalty if you file an amended return” was False. Even with a voluntary amended return, delinquency tax normally applies for the days the payment was late (less than ¥1,000 is rounded down to zero). The waiver of the additional tax for underreporting is limited to the case where you correct the mistake yourself before foreseeing a reassessment and before the advance notice of an audit. After the notice, but before foreseeing a reassessment, the rate is 5% (10% on the portion above the threshold). An amended return filed after foreseeing a reassessment (for example, after an audit) is 10% (15% on the same portion). If you file an amended return after concealment or disguising has been found in an audit, the 35% heavy additional tax is not reduced.

An amended return is a procedure that can reduce your burden. To keep the burden down, correct early, hide nothing, and pay on the day you file.

Sources

• ［1］Act on General Rules for National Taxes, Article 19 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［2］Act on General Rules for National Taxes, Article 23 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［3］Act on General Rules for National Taxes, Article 60 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［4］Act on General Rules for National Taxes, Article 65 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［5］Act on General Rules for National Taxes, Article 66 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［6］Act on General Rules for National Taxes, Article 68 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［7］Act on General Rules for National Taxes, Article 119 (e-Gov Law Search, Japanese)　Checked: 2026-10-05
• ［8］NTA Tax Answer No.2026 “When you made a mistake in your final tax return” (Japanese)　Checked: 2026-10-05
• ［9］NTA Tax Answer No.9205 “About delinquency tax” (Japanese)　Checked: 2026-10-05
• ［10］NTA, “Outline of the revision of the additional tax system (Act on General Rules for National Taxes)” (PDF, Japanese)　Checked: 2026-10-05
• ［11］NTA, “How to calculate delinquency tax” (Japanese)　Checked: 2026-10-05
• ［12］NTA, “Handling of additional tax for underreporting and additional tax for failure to file for self-assessed income tax and special income tax for reconstruction (administrative guideline)” (PDF, Japanese)　Checked: 2026-10-05

Note: This article is based on laws and official information as of October 5, 2026. It is a translation of the Japanese original; if the two differ, the Japanese version prevails. Quotations from laws and official sources are given in the original Japanese, followed by unofficial reference translations. Sources are limited to laws (e-Gov) and official NTA pages, all in Japanese. If a correction is needed after publication, a correction record will be added at the end of this article (Correction policy).