Redoing the Year-End Tax Adjustment: the January Deadline

This is a translation of the Japanese original. The Japanese version is authoritative; figures follow Japanese tax law.

It happens after the year-end tax adjustment (nenmatsu chosei) is over: you notice a deduction you forgot to claim, or an estimate that turned out wrong. National Tax Agency (NTA) materials give the employer only one deadline for redoing it. The end of January of the following year, the point by which the withholding tax statement (gensen choshu-hyo) has to be issued to the employee. But that deadline covers the direction in which you were over-taxed. In the opposite case, where too much was deducted and the tax falls short, the employer has to redo the calculation and collect the shortfall even after the end of January. The first year of the housing loan deduction, the medical expenses deduction, furusato nozei (furusato nozei) and the casualty loss deduction cannot be handled by the employer at all, so you file a tax return yourself. One missing life insurance premium certificate is worth about ¥11,000; a wrong estimate for the special spousal deduction moves ¥77,596. And if you miss the employer's window, a refund claim can still reach back five years from 1 January of the following year.

The short answer: four boxes, set by when you noticed and which way the tax moves

When you noticed	Too much tax taken (money comes back)	Not enough tax taken (money is owed)
By the end of January of the following year	Tell your employer and the year-end adjustment is redone. The difference is refunded through your pay	The employer redoes it and collects from your pay
After the end of January of the following year	The employer's window has closed. File a tax return yourself (a refund claim reaches back five years)	The employer has to redo it even after the end of January

Sources: NTA, "How to do the year-end tax adjustment for 2026" (Reiwa 8-nen-bun Nenmatsu Chosei no Shikata), page 43[NTA, year-end adjustment guide 2026]; NTA Tax Answer No.2671[NTA No.2671]

The most important thing in this table is that the bottom-left and the bottom-right do not match. The window for having your employer give back what was over-collected closes at the end of January. The redo that collects a shortfall has no deadline at all. The NTA states it plainly: it "must be carried out even on or after the end of January of the year following the year in which the change occurred"[NTA No.2671].

It is asymmetric, but the road back is not closed. Even if the employer does nothing, a tax return can reach back five years from 1 January of the following year[NTA No.2030].

The employer's only deadline is the end of January of the following year

Page 43 of the NTA's "How to do the year-end tax adjustment for 2026" lists six situations that arise after the adjustment, and attaches the same sentence to all five of them other than an additional salary payment within the same year. "This redoing of the year-end tax adjustment is possible only up to the end of January of the following year, the point by which the 'withholding tax statement for employment income' has to be issued to the recipient."[NTA, year-end adjustment guide 2026]

The five situations in which the employer can redo it (from the NTA's headings)

The number of dependent relatives changed after the adjustment (a child married and left your dependents, you yourself became a person with a disability, and so on)
The estimated income of the spouse or of you differed from the figure used for the spousal deduction or the special spousal deduction
The estimated income of a specified relative differed, where the special deduction for specified relatives (tokutei shinzoku tokubetsu kojo) was applied
You paid a premium after the adjustment (life insurance or earthquake insurance)
The declaration for the special deduction for housing loans (jutaku shakuirekin-to tokubetsu kojo shinkokusho) was submitted after the adjustment (second year onwards)

Conversely, the treatment is cold when the certificate does not turn up in time. Where the deduction was applied on the condition that the certificate would be handed in, and it does not arrive by the end of January, the employer recalculates without that premium and collects the shortfall[NTA, year-end adjustment guide 2026]. Leave the envelope sitting on your desk and you get an extra deduction from your pay, not a refund.

Why the redo happens in the first place

Because the day the test is applied and the day the sum is worked out are different. The Income Tax Act judges dependent relatives by the situation on 31 December of that year. The year-end adjustment, meanwhile, is carried out when the last salary of the year is paid[NTA No.2671]. If a marriage, a birth or a first job happens after the numbers were closed in early December, the answer changes. The redo is not an exception; it is an ordinary procedure built into the system.

The division of labour between the year-end adjustment and the tax return is set out in the difference between the year-end adjustment and the tax return.

Case by case: tell the employer, or file yourself

What you noticed	What to do	Does the tax move
The life insurance premium certificate did not reach the year-end adjustment in time	To the employer if it is still January. After that, a tax return	Comes back (about ¥11,000 in the worked example below)
A child was born at the end of the year	Hand the dependent declaration form to the employer	Income tax does not change (children under 16 are outside the dependent deduction)
You married in December and your spouse has almost no income	To the employer if it is still January	Comes back (the spousal deduction is added)
Your spouse's annual income was higher than estimated	Tell the employer. The employer redoes it even after the deadline	You owe more (¥77,596 in the worked example below)
Your spouse's annual income was lower than estimated	To the employer if it is still January. After that, a tax return	Comes back
A child started work and left your dependents	Report the change to the employer	You owe more
The first year of the housing loan deduction	The employer cannot handle it. File a tax return	Comes back
You forgot to hand in the declaration for the housing loan deduction, second year onwards	To the employer if it is still January. After that, a tax return	Comes back
A pay rise was agreed in the following year and paid retroactively to cover the current year	No redo needed	It becomes income of the year in which the revision was made

Sources: NTA, "How to do the year-end tax adjustment for 2026", page 43; NTA Tax Answer No.2671 and No.2030.

The one most often misunderstood is "a child was born at the end of the year". A child under 16 does not qualify for the dependent deduction. Redo the year-end adjustment and your income tax falls by exactly nothing. Hand in the dependent declaration form all the same. It feeds into the resident tax exemption test in later years, and into benefits that carry an income limit. How to fill the form in is set out in how to fill in the dependent deduction declaration.

Five things the employer can never handle

Fixable through the employer's redo

A change in the number of dependent relatives (judged as at 31 December)
A wrong estimate for the spousal deduction or the special spousal deduction
A wrong estimate for the special deduction for specified relatives
A late certificate for the life insurance or earthquake insurance premium deduction
The housing loan deduction from the second year onwards (a declaration handed in late)

Only fixable by filing a tax return

The first year of the housing loan deduction
The medical expenses deduction
The donation deduction (furusato nozei and the like)
The casualty loss deduction (disaster, theft)
The deduction for specified expenses of employment income earners

Source: NTA Tax Answer No.2030, "Refund claims"[NTA No.2030]

Furusato nozei alone needs a footnote. It is true that the year-end adjustment cannot handle it, but that does not make a tax return compulsory. If your One-Stop Exception (one-stop tokurei) applications went through, the amount is deducted from your resident tax without any tax return. If you forgot to apply, or if you are filing a return anyway for something like the medical expenses deduction, put the donation deduction on that return too.

How much is at stake: two worked examples

Example 1: the life insurance premium certificate was never handed in (deduction of ¥40,000, taxable income of ¥4 million / this site's estimate)

Income tax: ¥40,000 × 20% = ¥8,000. With the 2.1% special income tax for reconstruction, ¥8,168
Resident tax: deduction of ¥28,000 × 10% = ¥2,800
A total of about ¥10,968 never comes back

Note: the resident tax life insurance premium deduction has a lower ceiling than the income tax one, and ¥28,000 for a new contract was used here. Check the ceiling with your own municipality. The 20% income tax rate on taxable income of ¥4 million comes from the quick tax table in the NTA's "How to do the year-end tax adjustment for 2026".

Example 2: a special spousal deduction of ¥380,000 was applied, but the spouse's income exceeded the estimate and the deduction fell to zero (taxable income of ¥4 million / this site's estimate)

Extra income tax owed: ¥380,000 × 20% = ¥76,000
With the 2.1% special income tax for reconstruction, ¥77,596
The employer has to redo the calculation and collect it even after the end of January

One missing certificate is ¥10,000-odd; a wrong estimate of a spouse's income is in the ¥70,000s. Example 2 in particular does not go away if you ignore it. In a year when your spouse picked up extra hours towards December, checking the annual figure on the December payslip is the safe move.

When and how much the year-end adjustment gives back is covered in when and how much the year-end adjustment refund comes to. If the "withholding tax amount" on your withholding tax statement is zero, there is no tax there to give back. A refund needs income tax that was withheld or paid as an estimated payment[NTA No.2030].

What to do when you have missed the window

Get your withholding tax statement out. Check four figures on it: the amount paid, the amount after the employment income deduction, the total of income deductions, and the withholding tax amount.
Collect the certificates for the deductions you missed. Life insurance premium certificates, earthquake insurance premium certificates, certificates for National Pension contributions and so on. Ask the insurer or the pension office for a reissue.
Prepare the tax return. Enter the figures from the withholding tax statement and add the deductions that were left out.
Check the deadline. A refund claim can be filed for five years from 1 January of the year following that year[NTA No.2030]. For the 2026 tax year that means up to 31 December 2031.
If you spot the error after you have already filed a return, it is a different procedure. The difference is sorted out in amended returns versus requests for correction.

Summary

You can have your employer redo your year-end adjustment only until the end of January the following year, and only to correct an overpayment.
If too much deduction was applied and tax is underpaid, the company will redo the adjustment and collect the shortfall even after January 31.
The first year of the housing loan deduction, the medical expense deduction, furusato nozei, and the casualty loss deduction cannot be processed by the company - these require a final tax return.
Forgetting to submit just one life insurance premium certificate can shift tax by about ¥11,000, and a misestimate on the spousal special deduction can shift it by ¥77,596.
Even if you miss the deadline, a refund claim can go back 5 years from January 1 of the following year; for the 2026 (Reiwa 8) tax year, that's until December 31, 2031.

Sources

NTA, How to do the year-end tax adjustment for 2026 - page 43, "Re-adjustment where additional salary was paid or dependent relatives changed after the year-end adjustment". The deadline for the redo, the five situations, the case of a certificate that never arrived, and the treatment of retroactive pay
NTA Tax Answer No.2671, When the number of dependent relatives changes after the year-end adjustment - the test applies as at 31 December, and a redo for a tax shortfall must be carried out even on or after the end of January
NTA Tax Answer No.2030, Refund claims - a refund claim runs for five years from 1 January of the following year, and the medical expenses deduction, the first year of the housing loan deduction, the donation deduction and the casualty loss deduction all need a tax return

Note: the worked examples in this article apply the NTA's quick tax table and the structure of the deductions as this site reads them; they are not calculation examples published by the NTA. This is general information. For an individual decision, check with your employer's payroll staff, a tax office or a tax accountant.