Year-End Adjustment vs. Kakutei Shinkoku: Which You File
Most employees never file: the December year-end adjustment inside payroll settles the whole year. But side income over 200,000 yen, a second payer, first-year mortgage paperwork, or medical bills over 100,000 yen move you into the February to March filing window. This guide sorts all three buckets: adjustment suffices, filing required, filing beneficial.12
Procedures, fees, and requirements can change. Confirm current details at the National Tax Agency site. This article is general information, not tax advice; for your specific case, consult a licensed tax accountant (zeirishi).
Overview
The decision has exactly three outcomes. Either the 年末調整 (nenmatsu chosei, "year-end adjustment") at your employer ends the year, or the NTA requires a 確定申告 (kakutei shinkoku, "final tax return"), or no rule forces a return but filing one pays you back.12 Find your bucket first; the paperwork follows.
The chart compresses the NTA required-cases list into one decision path; thresholds below are dated to current guidance (as of 2026-09).1
Year-end adjustment suffices
One employer, employment earnings of 20,000,000 yen or less, other income of 200,000 yen or less, and no special claims outside payroll: December settles everything and no return exists (as of 2026-09; confirm current figures with the NTA).1 This is the default salaried life the payroll system was built for, and the mechanics of withholding tables and December reconciliation belong to the companion payroll article rather than this decision guide.
You must file
The 200000 yen side-income line
With a single salary source, non-employment and non-retirement income over 200,000 yen in the year forces a return (as of 2026-09).1 The test runs on net income after expenses, not on gross receipts, and it excludes employment and retirement income by definition.1
With two or more salary sources, the test widens: non-primary salaries plus other income over 200,000 yen combined forces the return (as of 2026-09).1 Employment earnings over 20,000,000 yen from any configuration force it independently of side income (as of 2026-09).1
A full-time job plus weekend contracting is the classic accidental filing case. Neither stream alone crosses the line, but their sum does, and the NTA tests the sum.1
First-year mortgage, medical over 100000, and other triggers
The first year of the housing-loan credit always requires a tax-office filing with the house documents; only from the second year can payroll carry it.3 Medical-expense relief, or 医療費控除 (iryohi kojo), works the same exclusive way: spending above 100,000 yen in the year, or above 5 percent of income where income sits under 2,000,000 yen, up to a 2,000,000 yen deduction cap, is deductible only through a filed return with the medical-expense statement attached (as of 2026-09).4
Further required cases complete the NTA list: casualty-loss claims, gains on property sales, retirement income with special claims, certain foreign-source income configurations, and departure filings for leavers.15 Each has its own forms, but all share the same February to March window: for 2025 income, February 16 to March 16, 2026 (as of 2026-09).6
Filing when you do not have to: the beneficial cases
Medical spending over the floor often produces a refund even where nothing required a return: the adjustment cannot carry medical costs, so December over-withheld against a liability the return then shrinks (as of 2026-09).4 Mid-year resignation works the same way in reverse: with no December employer to run the adjustment, months of withholding calibrated to a full year stand against a part-year liability, and a return recovers the difference as a typical outcome.
The rule of thumb: a required filing avoids penalties, but a beneficial filing chases money. Both use the same window and the same forms.
Foreign income and departure filings
Foreign-source income can force a return depending on residency status and how the funds moved, and leaving Japan triggers its own filing plus tax-administrator mechanics.15 The characterization detail belongs to the treaty guide and the departure guide; what matters for this decision is that overseas income never defaults to the adjustment-suffices bucket without checking.
A US taxpayer in Japan can owe a Japanese return under this article's tests and a US return under citizenship rules in the same spring. Keep both calendars, and keep the Japanese assessment receipts for the foreign-tax-credit claim.
Good to know
Two payers means checking the line every year
The multi-source test combines non-primary salary with other income against the same 200,000 yen line (as of 2026-09).1 A job change mid-year, a bonus from an old employer, or a first freelance invoice can each tip a previously safe year over the line.
Medical filing needs the statement, not the shoebox
The return requires the medical-expense statement aggregating providers and amounts; loose receipts alone do not complete the claim.4 Build the statement through the year rather than reconstructing it in March.
A missed required filing compounds at renewal time
Proper performance of public duties including tax is a stated criterion for permanent residence, and even late-paid amounts count against the applicant in principle (as of 2026-02-24).7 An unfiled required return is worse than a late payment: file, even late, rather than waiting to be found.
See also
- Withholding and Year-End Adjustment in Japan
- Client-Side Withholding (Gensen Choshu)
- Side-Business While Employed: What's Allowed
- Blue-Form vs. White-Form Tax Returns
- Final-Year Tax Filing and the Nozei Kanrinin
- US-Japan Tax Treaty: Mechanics and Pitfalls