The Furusato Nozei Cap: Why It Isn't About Your Salary

Quick Answer: Your cap is not a function of salary. It is a function of your resident tax, and specifically of one limit: the special-portion deduction cannot exceed 20% of your 住民税所得割額. Which means every other deduction you claim — iDeCo, insurance, dependants, a housing loan — quietly shrinks your Furusato Nozei cap.

Every Furusato Nozei article tells you to check your cap. Almost none explain what the cap actually is, which is why two colleagues on identical salaries compare numbers, find they differ by tens of thousands of yen, and assume one of them made a mistake.

Neither did. The cap was never about salary.

This is educational information, not tax advice. Confirm your own position with your municipal office or a qualified Japanese tax professional.

What is the cap actually made of?

Furusato Nozei is not one deduction. It is three, and the Ministry of Internal Affairs and Communications sets them out separately:

Formula
1. Income tax (donation − ¥2,000) × your income tax rate
2. Resident tax, basic portion (donation − ¥2,000) × 10%
3. Resident tax, special portion (donation − ¥2,000) × (100% − 10% − your income tax rate)

Add those three together and they come to the full donation minus ¥2,000. That is the whole trick — the ¥2,000 is what is left over when the three deductions have done their work.

Note what is doing the heavy lifting. The special portion is by far the largest of the three, because it picks up everything the other two don't. And it is the only one with a ceiling.

What is the limit that actually binds?

This one sentence is the entire cap:

「特例分の計算結果が住民税所得割額の２割を超える場合は…（住民税所得割額）×20％」

If the special portion would come to more than 20% of your 住民税所得割額 — your income-based resident tax — it is cut to exactly that. Yokohama's guidance adds the precision that the 20% applies to the 所得割額 after the 調整控除 has been applied.

So the binding constraint on your Furusato Nozei cap is 20% of a resident tax figure. Not your gross salary. Not your take-home. A specific line on a tax bill most people never read.

Once the special portion is capped, extra donations stop being reimbursed in full — you keep the gift, but your out-of-pocket rises above ¥2,000 for every yen beyond the line. That is what "going over your cap" actually means.

Why do iDeCo and other deductions shrink your cap?

Here is the consequence almost nobody mentions, and it is genuinely counterintuitive.

Your 住民税所得割額 is calculated after your deductions. So anything that lowers your resident tax also lowers the number the 20% is taken from — and therefore lowers your Furusato Nozei cap.

That includes:

None of this makes those deductions bad — they save you far more than they cost you in Furusato capacity. But it does mean the two interact. Max out iDeCo and your Furusato cap comes down. Have a dependent spouse and a child and your cap is materially lower than a single colleague on the same salary.

It also explains the timing problem: your deductions for the year are not final until the year is, which is why donating to roughly 80% of an estimate is the standard advice rather than pushing to the edge.

Why don't the online calculators agree with each other?

Because they are all rearranging the same three formulas into a single line, and the rearrangement involves your marginal income tax rate — which brings in the reconstruction surtax, bracket boundaries, and the 調整控除. Small differences in how each tool handles those produce different answers.

The Ministry publishes the deduction mechanism above; it does not publish a one-line "your cap is X" equation. Any site presenting one has derived it. That is not dishonest — it is just worth knowing that the number you get is an estimate built on assumptions about your deductions, and that your own 源泉徴収票 is the only thing that settles it.

Which is the practical answer: use a simulator to get a range, not a decimal. Ours is the Furusato Nozei Simulator, and the full programme — deadlines, One-Stop, the documents — is in Furusato Nozei in English.

What does this mean if you're new to Japan?

Two things follow directly from the cap being a resident tax figure.

In your first calendar year you usually have no cap at all, because resident tax is charged on the previous year's income and you had none in Japan. There is nothing for the donation to reduce.

In your second year your cap appears but is small, because it is based on a partial first year of income. It reaches its normal level in year three. For how resident tax behaves across those first years, see how much of your Japan paycheck can go toward FI.

Frequently Asked Questions

How is the Furusato Nozei limit calculated?

Through three deductions — income tax at your marginal rate, resident tax at 10%, and a special portion covering the remainder — which together return your donation minus ¥2,000. The limit comes from a ceiling on the third: the special portion cannot exceed 20% of your 住民税所得割額, applied after the 調整控除.

Why is my Furusato Nozei cap different from a colleague on the same salary?

Because the cap is based on resident tax, not salary. Dependants, iDeCo contributions, insurance premium deductions, a housing loan credit and medical expenses all reduce your resident tax — and therefore reduce the figure the 20% limit is taken from.

Does iDeCo reduce my Furusato Nozei limit?

Yes. iDeCo contributions are deductible, which lowers your 住民税所得割額, which lowers the cap. The iDeCo deduction is still worth considerably more than the Furusato capacity it costs you, but if you are modelling both, model them together rather than separately.

What happens if I donate more than my cap?

You keep the gift, but the excess is no longer fully offset. Your out-of-pocket cost rises above ¥2,000 by roughly the amount you exceeded the limit, so over-donating is the most expensive mistake available in the programme.

Can I use Furusato Nozei in my first year in Japan?

Usually not. The cap derives from resident tax, which is charged on the prior year's income — so a first-year arrival typically has nothing to reduce. Most foreign employees become useful participants in their second year, and reach a normal cap in their third.

PlanTogetherFI is for educational planning only. It is not tax, financial or legal advice. Caps depend on income, deductions, family situation, municipality and year, and the figures above describe the mechanism rather than your personal limit — confirm with your municipal office or a qualified Japanese tax professional.

Sources and further reading

Rules reflect the position as of August 2026 and can change. Confirm your own cap with your municipal office.