SEISEI INSIGHTS — Family Wealth
Same Income, Different Tax Burden: How Sole Proprietorships and Corporations Are Taxed Differently
2026-06-19
"Isn't incorporating just one more layer of paperwork?" We hear this question repeatedly from sole proprietors whose income has grown. Yet earning income as an individual and conducting business through a company are governed by genuinely different tax structures. This article explains where that difference comes from — not in terms of how much tax is "saved," but as a matter of how the systems are built.
Three Structural Sources of the Difference
The differing outcomes between individuals and corporations can be grouped under three points:
- Employment income deduction — When you receive a director's remuneration (salary) from a company, employment income is computed by subtracting the employment income deduction from gross receipts (Income Tax Act, Art. 28). A sole proprietor's business income has no such deduction.
- Splitting the progressive structure — An individual's income is taxed as a single whole under the progressive schedule of Article 89 of the Income Tax Act (up to 45%). With a company as the earning entity, income divides into "the portion the individual receives as director's remuneration" and "the portion retained in the company," each handled under a different rate band and tax system.
- Scope of deductible expenses — Director's remuneration may be deductible where it meets certain requirements, such as being fixed periodic remuneration (Corporation Tax Act, Art. 34). Under those requirements, a company may treat a broader range of outlays as expenses than a sole proprietor can.
An Illustrative Model: ¥40 Million of Annual Income
The following is an approximate model meant only to show the direction of the structure. Actual figures vary with social insurance, individual deductions, and expense circumstances; specific tax amounts require calculation by a qualified professional.
| Item | Sole proprietor | After incorporation |
|---|---|---|
| Business income | ¥40M | ¥40M |
| Director's remuneration | — | ¥12M |
| Income & resident tax | ≈ ¥18M | Taxed on the remuneration portion |
| Corporate tax, etc. | — | Taxed on income retained in the company (23.2% basic rate) |
The basic corporate tax rate is 23.2% (Corporation Tax Act, Art. 66(1)), and the first ¥8 million of income for an SME is taxed at 19% (Art. 66(2)). Compared with an individual's top bracket, splitting income into director's remuneration and retained corporate profit makes it structurally harder for either portion to reach the top rate.
The Costs of Incorporating
Holding a company also carries its own costs:
- Social insurance — A company's directors must enroll in health insurance and the employees' pension.
- Closing and filing — A company must prepare annual financial statements and tax filings, which carry practical costs.
- Per-capita levy — A company owes the per-capita portion of corporate resident tax even when it operates at a loss.
Whether incorporation is structurally meaningful therefore depends on the balance between the scale of income and these ongoing costs. It is generally considered worth examining above a certain income level, though the break-even point depends on individual circumstances.
The Corporation as Foundation
The significance of incorporation is not limited to a single year's tax burden. Family shareholding structures, business succession, and transfers of assets to the next generation all presuppose the existence of a corporate entity. Structures that never arise as options for a sole proprietorship become examinable only with a company as the foundation. Incorporation is best understood as the groundwork supporting the whole of subsequent wealth design.
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.