Year-end adjustment guide
The documents, deductions, employer workflow, what it covers, and common employee mistakes.
Year-end adjustment is your employer applying your basic, spouse, dependent, social-insurance, and insurance deductions (plus the mortgage credit from year two) to reconcile your income tax — submit the declaration forms and insurance certificates on time.
Effective: 2026-01-01 to 2026-12-31
Professional review pending — treat as draft and confirm with the authorities.
Key points
- You submit declaration forms plus insurance and iDeCo certificates.
- It applies most common deductions but not medical, donations, or the first mortgage year.
- From the second year the mortgage credit can run through payroll.
- A former-employer certificate lets a combined adjustment happen.
Documents and deductions
You submit the basic/spouse/dependent declaration, the insurance-premium declaration with certificates, and (from year two) the mortgage-credit statement. The employer then applies the basic, spouse and spouse-special, dependent, social-insurance, and life/earthquake-insurance deductions and produces your withholding certificate. Small-business-mutual-aid and iDeCo contributions can be included with certificates.
What it misses
Year-end adjustment cannot handle the medical deduction, donations beyond one-stop, the first mortgage-credit year, or any non-salary income — those need a return. The most common mistakes are missing the submission deadline, forgetting an insurance certificate, and assuming the adjustment covers a side gig it does not.
Who this is for
- Employees completing year-end paperwork
- People new to the process
What this is not
- Medical/donation claims (file a return)
- If you have side income or medical costs, year-end adjustment is not enough — file a return.
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.