Residents of Canton Aargau are generally required to file an annual income tax return covering their worldwide income and assets (subject to applicable treaty rules and allocation between cantons and countries). This page explains who must file, which deadlines apply, how the filing process works and how the rules interact with withholding tax (Quellensteuer) for foreign nationals.

Who Must File an Income Tax Return in Aargau?

In principle, you must file an income tax return in Aargau if one of the following applies:

• You are resident in Aargau for tax purposes at the end of the tax year.
• You move to or from Aargau during the year and are resident for part of the year.
• You are self-employed and carry on a business in Aargau.
• You hold a permanent establishment or partnership interest in Aargau.
• You own real estate located in Aargau, even if you live in another canton or abroad (limited tax liability).
• You are subject to withholding tax but meet the conditions for a subsequent ordinary assessment.

Married couples and registered partners who live together are usually taxed jointly and file a joint tax return, which covers the income and assets of both spouses/partners and any dependent children.

Residents vs. Non-Residents

The filing obligation depends on your tax status:

• Residents of Aargau generally declare worldwide income and assets (with relief for foreign tax under treaty rules and unilateral relief provisions).
• Non-residents with limited tax liability in Aargau must typically declare only the income and assets that are taxable in Aargau (e.g. income from Swiss real estate or a permanent establishment located in the canton).

Interaction with Withholding Tax (Quellensteuer)

Foreign nationals who do not yet hold a permanent residence permit are often subject to withholding tax on employment income. In Aargau, this means:

• Your employer deducts tax directly from your salary using the applicable withholding tax tariff.
• You may still need, or be entitled, to a subsequent ordinary assessment in certain cases, for example:
  • If your income exceeds a certain threshold,
  • If you have significant additional income or assets, or
  • If you wish to claim deductions that are not fully reflected in the withholding tariff.

In such situations, the tax authorities may require you to file a full tax return. The withholding tax already paid will be credited against the final tax due; this can result in additional tax to pay or a refund, depending on your circumstances.

Filing Deadlines

Aargau, like other cantons, sets annual deadlines for filing the income tax return. In general:

• Tax returns are filed for each calendar year.
• The ordinary filing deadline falls some months after the end of the tax year.
• Deadlines may differ for individuals and legal entities.

The exact filing deadlines can change from year to year and may depend on whether you file on paper or electronically. Taxpayers who cannot meet the ordinary deadline can usually request an extension, provided this is done in good time.

Extensions of Time

If you are unable to submit your tax return by the ordinary deadline, you can typically apply for an extension of time. In practice:

• Extensions must generally be requested before the original deadline expires.
• They are often granted for a limited additional period.
• Further extensions may be possible in justified cases (e.g. illness, complex situations, delayed documents).

If you work with a tax advisor, the advisor may coordinate extensions on your behalf under the local administrative practice.

Documents and Information Required

To complete your Aargau tax return accurately, you usually need to gather the following documents and information (non-exhaustive):

• Salary certificates (Lohnausweise) for all employments,
• Statements of self-employment income and business accounts (if applicable),
• Bank and investment statements as at year-end,
• Information on real estate owned in Switzerland and abroad (rental income, imputed rental value, mortgages),
• Evidence of deductible expenses (commuting costs, professional expenses where applicable),
• Proof of pension contributions and social security payments,
• Insurance premium statements (where relevant for deductions),
• Information on children and dependants (birth dates, custody, support payments),
• Details of foreign income and foreign tax paid (for treaty relief and avoidance of double taxation).

Depending on your situation, additional documents may be required (e.g. partnership or company documentation, trust or foundation information, cross-border employment certificates).

New Arrivals and Departures

Special filing considerations apply if you:

• Move to Aargau from another canton or from abroad during the year, or
• Leave Aargau during the year for another canton or another country.

In such cases, the tax year may effectively be split between different cantons or between Switzerland and a foreign jurisdiction. Aargau will generally tax income attributable to the period of residence or limited tax liability in the canton. The tax return must accurately reflect arrival and departure dates and any change of residence within Switzerland.

Self-Employed Persons and Business Owners

If you are self-employed or carry on a business in Aargau, you will typically:

• File a tax return including your business income and assets,
• Submit basic accounts (profit and loss statement, balance sheet) and supporting documentation,
• Be subject to both income tax and, where relevant, capital tax on business assets.

The filing obligations for self-employed persons can be more complex than for employees, making early preparation and professional advice particularly important.

Real Estate Owners

If you own real estate in Aargau, you will generally have to declare:

• Rental income or imputed rental value of the property,
• Mortgage interest and permissible property-related deductions,
• The taxable value of the property for wealth tax purposes.

Even if you are resident in another canton or abroad, owning property in Aargau can trigger a filing obligation due to limited tax liability in the canton.

Consequences of Late or Non-Filing

Failing to file a tax return or filing late may result in:

• Reminder letters and administrative fees,
• Estimated assessments by the tax authorities,
• Possible penalties or interest on late payments.

It is therefore advisable to respect deadlines, request extensions when needed and ensure that your tax return is complete and accurate.

Practical Considerations

In practice, many taxpayers in Aargau:

• Use the official tax software or online platform provided by the canton,
• Keep a dedicated file for tax-relevant documents throughout the year,
• Seek professional advice in cross-border or complex income/asset situations.

The filing requirements in Aargau should always be considered together with the applicable rules on rates, deductions, special rules and the practical examples in order to understand the overall impact on your personal tax position.