What to do if you made a mistake on your tax return
Amended returns, requests for correction, supporting records, and deadlines.
If you paid too little, file an amended return (修正申告); if you paid too much, file a request for correction (更正の請求) — generally within five years — and a voluntary correction before an audit notice avoids the ordinary understatement penalty.
Effective: 2026-01-01 to 2026-12-31
Professional review pending — treat as draft and confirm with the authorities.
Key points
- Underreported tax → amended return (修正申告).
- Overreported tax → request for correction (更正の請求), generally within five years.
- Voluntary correction before an audit notice avoids the understatement penalty (interest may remain).
- A wrong resident-tax notice is fixed with the municipality, not the tax office.
Fixing an error
If you understated tax, file an amended return and pay the difference; if you overstated it, file a request for correction to reclaim the excess, generally within five years of the original deadline. Attach the records that support the change. If the mistake was in a payer’s withholding certificate, ask the payer to correct it before adjusting your return.
Penalties and timing
A voluntary correction made before the tax office contacts you generally avoids the understatement penalty, though delinquent interest can still apply for the period the tax was unpaid. The sooner you correct, the lower the cost. For a resident-tax notice error, contact your municipality — the national tax office cannot fix a municipal assessment.
Who this is for
- Anyone who spotted an error after filing
- People who received a correction notice
What this is not
- Deliberate concealment (get professional representation)
- If the error is large or involves omitted income, consult a 税理士 before responding.
Frequently asked questions
Do I need to file a tax return in Japan?
Many employees do not, because tax is settled by year-end adjustment (年末調整). You generally must file (確定申告) if you have side income over ¥200,000, two or more employers, self-employment income, sizeable investment or crypto gains, or you want to claim deductions like large medical costs or a first-year mortgage credit. Filing season is Feb 16 – Mar 15 via e-Tax. When unsure, check the NTA guidance or ask a 税理士.