Solothurn Corporate Income Tax
Last updated: 11 Dec 2025
Solothurn Corporate Income Tax — Profit Tax Rules
How corporate income tax works in the Canton of Solothurn: who is subject to profit tax, how the tax base is derived from accounting profit, how cantonal, communal and federal components interact, and what to know about Solothurn’s STAF instruments, participation relief and loss carryforwards.
Scope & Taxpayers
- Resident companies. Companies with statutory seat or effective place of management in Solothurn are subject to unlimited tax liability on their worldwide income, with relief or exemption for foreign permanent establishments and immovable property under double tax treaties and intercantonal rules.
- Nonresident entities. Nonresident companies are limited tax liable in Solothurn if they have local business operations, a permanent establishment, or Solothurn–situs real estate or business assets. Only profits attributable to the Solothurn nexus are taxed.
- Juristic persons only. The corporate income tax described here applies to juristische Personen (AG, GmbH, cooperatives and certain foundations and associations). Partnerships and sole proprietors are taxed at shareholder/owner level under personal income tax and are not the focus of this page.
- Tax period. The profit tax period for juristic persons generally follows the financial year. A change of year-end or an extended first business year should be coordinated with the Solothurn tax office.
Tax Base: From Accounting Profit to Taxable Profit
Solothurn corporate income tax is levied on the company’s taxable profit, determined by starting from statutory financial statements (usually Swiss GAAP FER or Code of Obligations accounts) and then making tax adjustments.
| Step | Description | Typical adjustments |
|---|---|---|
| 1. Accounting profit | Profit after tax per statutory financial statements for the relevant business year. | Profit as approved by the shareholders’ meeting, before appropriation of retained earnings. |
| 2. Add-backs | Non-deductible or partially deductible expenses are added back to profit. | Hidden profit distributions; excessive interest or royalties to related parties; non-business expenses; penalties; corporate income tax itself; certain provisions and value adjustments. |
| 3. Deductions | Items that are tax deductible but not expensed, or expensed differently, are deducted. | Tax-allowed depreciation that exceeds accounting depreciation (within cantonal limits); specific provisions; participation relief; patent box reduction; additional R&D deduction where applicable. |
| 4. Allocation & exemptions | Profits allocable to other cantons or foreign permanent establishments are exempt in Solothurn under intercantonal and treaty rules. | Profit/loss attribution keys (e.g. payroll, assets, turnover); separate determination of foreign PE income; treaty exemptions or credit methods. |
| 5. Taxable profit | Result after adjustments, before loss carryforwards and special reliefs. | Loss carryforwards of up to 7 years can be offset against current-year taxable profit (subject to standard Swiss rules and anti-abuse provisions). |
The Solothurn tax book (Steuerbuch Kanton Solothurn) and cantonal practice notes provide detailed guidance on depreciation, provisions, hidden equity, participation relief, the patent box, the additional R&D deduction and other adjustments relevant for the tax base. In practice, a clear reconciliation from accounting profit to taxable profit is expected as part of the corporate tax return.
Rates & Effective Burden
Cantonal & communal profit tax
Solothurn applies a proportional profit tax rate on net income at cantonal level for capital companies and cooperatives. The resulting simple cantonal tax is then combined with the communal share via the commune’s tax factor, yielding a single cantonal/communal profit tax for juristic persons.
After the implementation of STAF, Solothurn moved to a proportional regime on all profits and gradually reduced effective profit tax. For standard companies, the combined effective corporate income tax rate (cantonal/communal plus federal) typically lies in the mid-teens to upper-teens, depending on the municipality, year and use of reliefs.
For up-to-date effective Solothurn profit tax burdens by location, see this hub’s Rates page and the official Solothurn company tax calculator .
Federal corporate income tax
In addition to cantonal/communal profit tax, companies pay Swiss direct federal corporate income tax at a flat rate of 8.5% on profit after tax. Because federal tax itself is deductible, this corresponds to an effective rate of around 7.8% on profit before tax.
The combined effective corporate income tax rate in Solothurn is therefore the sum of:
- Cantonal/communal profit tax (based on the proportional cantonal rate and the communal factor); and
- Direct federal corporate income tax.
The Solothurn tax calculator on this hub allows you to model combined cantonal, communal and federal profit tax for a given level of taxable profit and different communes.
Participation Relief & STAF Measures
Solothurn follows federal rules for participation relief and has implemented a broad STAF toolbox at cantonal level. This toolbox can materially reduce the Solothurn profit tax base where conditions are met.
| Mechanism | Overview | Typical planning aspects |
|---|---|---|
| Participation relief | Qualifying dividends and capital gains from shareholdings in subsidiaries benefit from participation relief, reducing the tax burden via a deduction calculated on the basis of net participation income relative to total profit. | Minimum participation thresholds (e.g. 10% or CHF 1 million market value); holding period requirements; treatment of write-downs and liquidation proceeds; interaction with foreign withholding tax and treaty relief. |
| Patent box | Solothurn has introduced a patent box with a high relief level (up to 90% reduction on qualifying patent income at cantonal level), subject to OECD nexus requirements and detailed tracking of R&D expenses. | Identifying eligible IP; segregating IP income and costs; documenting the nexus between Solothurn R&D and the patents; coordinating patent box entry costs and step-up rules; use of rulings to confirm methodology. |
| R&D super-deduction | Solothurn allows an additional deduction of up to 50% on qualifying R&D expenditures on top of the booked expense, reducing the profit tax base for companies with material development activity. | Defining qualifying R&D based on Solothurn practice; distinguishing in-house vs. outsourced R&D; managing cost-plus arrangements; aligning documentation with the Swiss tax conference guidance. |
| Capital tax relief & notional elements | Under Solothurn’s STAF implementation, only a small percentage of equity attributable to qualifying participations, patents and certain intra-group loans is included in the capital tax base, significantly reducing capital tax for holding and IP-rich structures. | Identifying qualifying assets; tracking equity attributable to participations, IP and group loans; modelling the interaction between lower capital tax and profit tax reliefs; testing different financing structures. |
The overall relief from participation deduction, patent box, R&D super-deduction and capital tax relief is subject to a relief cap at cantonal level (maximum percentage reduction of the Solothurn tax base). For larger businesses, advance tax rulings are common to coordinate Solothurn and federal treatment and to document the STAF toolbox.
Losses, Groups & Permanent Establishments
- Loss carryforwards. Tax losses can generally be carried forward for up to 7 years and offset against future taxable profits in Solothurn. There is no loss carryback. In reorganisations or changes of ownership, special rules may restrict the use of losses.
- Group situation. Switzerland has no fiscal unity or tax consolidation for ordinary corporate income tax. Each Solothurn legal entity files its own return; group effects are managed via financing structures, transfer pricing, participation relief and, where relevant, STAF instruments.
- Intercantonal allocation. Where a company has operations, real estate or permanent establishments in several cantons, profit and capital are allocated using generally accepted keys (e.g. payroll, assets, turnover) based on practice and jurisprudence.
- Foreign permanent establishments. Under many double tax treaties, profits attributable to foreign permanent establishments are exempt in Switzerland with progression. Accurate attribution of profits and capital to PEs is essential to support the exemption.
- Restructurings. Mergers, de-mergers, contributions in kind and migrations of seat can be tax neutral if Swiss conditions are met (continuity of business, carry-over of hidden reserves, adequate consideration, etc.). Rulings are often used to secure treatment for Solothurn and federal purposes, especially where material hidden reserves or losses are involved.
Interaction with Capital Tax
Corporate income tax and capital tax are closely linked in Solothurn. Profit tax is levied annually on taxable income, while capital tax is levied on the company’s equity. Both are assessed based on the same tax return for juristic persons.
- The level and structure of equity influences the company’s overall tax burden: higher equity increases capital tax, but may reduce thin-capitalisation risks and related-party interest recharacterisation for profit tax purposes.
- Under Solothurn’s STAF rules, participations, patents and certain intra-group loans are only partially included in the taxable capital base, lowering capital tax on holding and IP-heavy structures and increasing the relative weight of profit tax.
- In Solothurn, profit tax can be credited against capital tax in certain circumstances, so the latter may function as a minimum tax in low-profit or loss years.
- For details on capital tax rates and base, see the Solothurn capital tax page and the combined tax calculator.
Compliance Snapshot
This guide focuses on the substantive rules for corporate income tax in Solothurn. For procedural aspects — who files, which forms to use and which deadlines apply — see the dedicated Forms & deadlines page.
| Area | Key points |
|---|---|
| Filing | Annual corporate tax return for juristic persons, typically via eTax Solothurn JP, including profit tax and capital tax. Electronic submission is standard; the canton’s practice determines whether additional signed documents are required. |
| Deadline | Ordinarily around six months after year-end; extensions are commonly available on request (online within a standard window; further extensions by special request to the Solothurn tax office). |
| Documentation | Signed financial statements; profit-to-tax reconciliation; schedules for participation relief, patent box and R&D super-deduction; documentation on inter-company pricing and permanent establishments where relevant. |
| Assessments & objections | Combined assessments for cantonal, communal and federal tax; objection rights and deadlines are set out in the assessment notice. In complex or cross-border cases, advance rulings and proactive dialogue with the Solothurn tax administration are common. |
FAQs
How high is the corporate income tax rate in Solothurn?
Solothurn applies a proportional profit tax rate at cantonal level, combined with the commune’s tax factor and Swiss direct federal corporate income tax. For standard capital companies, the combined effective corporate income tax rate (cantonal/communal plus federal) is typically in the mid-teens to upper-teens, depending on the municipality, tax year and use of reliefs such as the patent box and R&D super-deduction. For concrete examples, see this hub’s Rates page and the official Solothurn company tax calculator.
What is the difference between profit tax and capital tax in Solothurn?
Profit tax is charged on the company’s taxable income for the year, while capital tax is charged on the company’s equity (share capital, reserves and hidden equity) attributable to Solothurn at the end of the year. Both are levied annually and assessed together, but they operate on different tax bases and rates. Capital tax can function as a minimum tax in low-profit or loss years.
Are dividends from subsidiaries fully taxed in Solothurn?
Qualifying participations can benefit from participation relief. This mechanism reduces the effective tax burden on net participation income (dividends and certain capital gains) based on a formula comparing participation income to total profit. Where the conditions are met, the effective Solothurn and federal tax on qualifying dividends can be reduced significantly.
How are losses treated for Solothurn corporate income tax?
Tax losses can generally be carried forward for up to seven years and offset against future taxable profits. There is no loss carryback. In restructurings or changes of ownership, Swiss and Solothurn rules may limit loss utilisation; advance tax rulings are often used where material loss carryforwards are involved.
Can I get a ruling on a planned structure or transaction in Solothurn?
Yes. Solothurn, like other Swiss cantons, offers advance tax rulings. These are commonly used for holding and financing structures, IP arrangements (including patent box use), reorganisations, and application of STAF instruments. A well-prepared ruling request can provide valuable certainty on the corporate income tax treatment and its interaction with capital tax and federal tax.
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