SEISEI INSIGHTS — Family Wealth
Composition, Not Size: What Actually Sets Your Effective Tax Burden in Japan
2026-09-23
"With income at this level, surely my rate is already pinned at the top." We hear this repeatedly from clients who have sold a business and now draw most of their income from share disposals and dividends. If you picture Japanese income tax as a single staircase that climbs as income rises, the assumption is a natural one.
But effective burden is not set by the size of income alone. It depends heavily on which taxation method the income belongs to — on its composition.
Two Rate Tables Running in Parallel
Japan's income tax contains two rate systems of fundamentally different character.
The first is aggregate taxation. Article 89(1) of the Income Tax Act divides taxable aggregate income into seven progressive brackets, topping out at 45% on the portion above ¥40 million. Local inhabitant tax is layered on top — 10% combined under the standard rates in Articles 35(1) and 314-3(1) of the Local Tax Act — for 55% in total.
The second is separate self-assessment taxation. Article 37-11(1) of the Act on Special Measures Concerning Taxation, covering capital gains on listed shares, and Article 8-4(1), covering dividend income on listed shares, both impose national income tax at 15% "notwithstanding the provisions of Articles 22 and 89 of the Income Tax Act, separately from other income." The statute names Article 89 and switches it off. These categories never travel along the progressive table at all. Local inhabitant tax is separated on the same basis, at 5% in each case (Local Tax Act, Supplementary Provisions, Arts. 35-2-2 and 33-2: 2% prefectural plus 3% municipal).
| Method | Income covered | National tax | Local tax |
|---|---|---|---|
| Aggregate taxation | Employment, business income, etc. | 5–45% progressive (Income Tax Act, Art. 89(1)) | 10% (Local Tax Act, Arts. 35(1), 314-3(1)) |
| Separate self-assessment | Capital gains on listed shares | 15% (Special Taxation Measures Act, Art. 37-11(1)) | 5% (Local Tax Act, Supp. Prov., Art. 35-2-2) |
| Separate self-assessment | Dividend income on listed shares | 15% (Special Taxation Measures Act, Art. 8-4(1)) | 5% (Local Tax Act, Supp. Prov., Art. 33-2) |
A reconstruction surtax of 2.1% of the income tax amount applies in addition (Reconstruction Funding Act, Art. 13).
The Mix Is the Rate
Because the two tables run in parallel, the combined burden is a weighted average. All-aggregate income approaches the ceiling; all-separate income converges toward 20.315% (15% income tax, 0.315% reconstruction surtax, 5% inhabitant tax); for everyone in between, the mix decides.
The upshot: within the aggregate system, higher income means a higher rate, but separately taxed income is taxed at a flat rate however large it grows. So what largely drives the combined burden is the share taxed on an aggregate basis — and the larger the separately taxed portion, the closer the combined burden moves to 20.315% (subject to the special provision below once the base income amount passes a threshold). This structure is what Japan's long-running policy debate has called the "¥100 million wall."
The Adjustment Already in Force
An adjustment to this structure already exists in current law: Article 41-19 of the Act on Special Measures Concerning Taxation, the special provision for taxation of a specified base income amount.
The article has three layers.
Paragraph 1 sets scope and computation. An individual whose base income amount for the year exceeds ¥330 million is a "person subject to the special provision," and income tax is imposed in an amount equal to 22.5% of the portion exceeding that threshold, less the base income tax amount for the year. This is not a flat minimum rate on everything, but a top-up: it bites only where ordinary computation produces less tax than 22.5% of the excess.
Paragraph 1 has been amended by the Act Partially Amending the Income Tax Act, etc. (Act No. 12 of 2026, promulgated 31 March 2026). From its entry into force on 1 January 2027, the threshold becomes ¥165 million and the rate 30%. Under Article 47 of that Act's supplementary provisions, the amended Paragraph 1 applies to income tax for 2027 and later years; 2026 and earlier years remain under the previous rule (¥330 million, 22.5%).
Paragraph 2 defines the base income amount. To aggregate income, retirement income and timber income, it adds dividend income on listed shares (Art. 8-4(1)), business income from land transfers, long-term capital gains, short-term capital gains, capital gains on unlisted shares (Art. 37-10(1)), capital gains on listed shares (Art. 37-11(1)), Japan-source share-transfer income of non-residents, and miscellaneous income from futures transactions — nine items in all. In other words, the financial income that the separate regime had moved off the progressive table is reassembled here for the purpose of this test. Note that the items are not a simple sum of income: items 1 and 2, for example, are computed as if Article 8-5(1) did not apply, and items 4 and 5 are taken after special deductions — each item carries its own statutory adjustments.
Paragraph 3 defines the base income tax amount, doing so separately for residents other than non-permanent residents, for non-permanent residents, and for non-residents — in each case, the income tax computed as if Paragraph 1 did not apply.
Defined for All Three Residency Categories
That Paragraph 3 defines the term across all three residency categories is a structural point worth knowing for anyone holding assets and a home across borders. On the text of the statute, the base income tax amount is defined separately for residents other than non-permanent residents, for non-permanent residents and for non-residents; the categories are not drawn by nationality. Which category applies, which income falls within that category's scope of taxation, and how that affects the test depend on individual facts, and need to be confirmed by a partner tax accountant.
Three Things to Establish First
What this question calls for first is not a projection but an accurate picture of the present.
- How does your income divide between the aggregate and separate systems? The burden rate is decided here.
- Which of the nine items in Article 41-19(2) do your income streams fall into? That determines how the base income amount presents.
- In which tax year do you place realization events? The test operates on the base income amount "for the year."
One further premise: as noted above, from the 2027 tax year the threshold becomes ¥165 million and the rate 30%. Which standard applies to which tax year is a starting assumption for any structural thinking.
Mapping the composition of income — not its size — onto a single structural diagram is where this question actually begins.
This article provides general information on tax systems and does not constitute individual tax consultation. Specific filings and tax computations are handled by licensed partner tax accountants whom we introduce.