Quellensteuer — How Source Tax Works and When You Should File a Return

The comfortable assumption: "my tax is deducted from my payslip, so my tax is done." Source tax makes taxation invisible, which is not the same as making it optimal. For some households the difference is a few hundred francs a year; for others it is thousands.

Who is taxed at source

Generally, foreign employees without a C permit (and not married to a Swiss citizen or C-permit holder) have tax withheld directly by the employer — the Quellensteuer. The rate comes from a cantonal tariff table keyed to your situation: single, married, sole earner, number of children, church affiliation.

First control question: is your tariff code correct? A marriage, a birth, a partner stopping or starting work — each changes the tariff. Employers apply what they know; they only know what you told HR. A wrong code runs silently for years and settles at the correction, in either direction.

The 120,000 threshold

Earn CHF 120,000 or more gross in a year and you are mandatorily reassessed through the ordinary tax process — you file a full return, and source tax already paid counts as a down payment. This continues in later years. For internationally mobile professionals crossing that line, the first ordinary assessment often lands as a surprise bill: the tariff assumed average deductions, your canton's reality was different.

Below the threshold: the voluntary filing decision

Below CHF 120,000 you can request a retrospective ordinary assessment — the deadline is 31 March of the following year, and the request is generally binding for future years too.

When filing tends to pay: substantial Pillar 3a contributions, pension buy-ins, high commuting or training costs, childcare deductions, debt interest. The tariff bakes in average deductions; if your actual deductions are above average, source tax overcharged you.

When it can backfire: the ordinary assessment considers your full situation — worldwide income and assets, a working spouse abroad, wealth tax. Filing to reclaim CHF 400 of 3a deduction and surfacing a wealth-tax liability is a real pattern. Run the whole household picture, not one deduction, before requesting it. Once requested, there is no going back to the simple tariff.

The cross-border layer

Source-taxed does not mean released from other obligations: foreign accounts, foreign property and foreign pension rights can still matter for Swiss taxation and for the country you left. Double-taxation treaties decide who taxes what — treaty questions are exactly where a one-hour consultation with a tax professional earns its fee.

What are you optimising for?

Source tax optimises for simplicity. An ordinary assessment optimises for accuracy. Which one favours you is a calculation, not a guess — and it changes when your salary, family or deductions change.

The household check: current tariff code confirmed correct · gross income vs the 120k line · last year's deductible items listed with amounts. With those three facts, the filing decision takes ten minutes. Without them, it defaults to "do nothing" — which is also a decision, just an unexamined one.