Correction vs. ordinary assessment
A correction fixes specific items within the source-tax system. Ordinary assessment (mandatory above ~CHF 120,000, voluntary on request in many cantons) applies the full deduction catalogue – often worthwhile with 3a contributions, high commuting costs or childcare. Caution: once assessed ordinarily, you usually stay in that system.
What's typically worth claiming
Pillar 3a payments, pension fund buy-ins, effective commuting and meal costs above the flat rates built into the tariff, childcare, and international weekly-residency situations.
Don't miss 31 March
Set the deadline as a recurring reminder – missed deadlines are the most expensive 'deduction' of all.
Track these costs in your own budget: create your free Swiss budget in BudgetHub – in English, with Swiss categories built in.
Who is taxed at source – and for how long
Source taxation (Quellensteuer) applies to employees without a settlement permit (C permit) and to those not married to a Swiss citizen or C-permit holder. The employer deducts the tax directly from salary using cantonal tariffs that already include standard deductions in flat form.
The flat form is the crux: the tariff assumes an average situation. If your actual deductions exceed that average – pillar 3a contributions, pension fund buy-ins, childcare, high commuting costs, further education – you have overpaid, and the difference is only recovered by filing.
Above a cantonal income threshold, ordinary assessment becomes mandatory rather than optional. Below it, you must request it – and that request has a deadline.
The deadline that quietly costs money
The request for a subsequent ordinary assessment (nachträgliche ordentliche Veranlagung) generally must be filed by 31 March of the year following the tax year. Miss it, and the source tax is final for that year regardless of how much you overpaid.
This single deadline is the most expensive detail in Swiss expat taxation. People who contributed to pillar 3a specifically for the tax benefit and never filed the request have paid the contribution without receiving the deduction.
Practical rule: if you paid into 3a, bought into your pension fund, had childcare costs or a long commute, file. The exercise takes an evening and is frequently worth a four-figure refund.
Once you file, you keep filing
Requesting ordinary assessment is not a one-off: in most cantons it applies for subsequent years too, and the source tax deduction continues as a prepayment against the final bill. This is not a disadvantage, but it changes the rhythm – returns become an annual routine.
It also means your tax outcome depends on your commune, not just the cantonal tariff. For high earners in a high-multiplier commune, ordinary assessment can produce an additional payment rather than a refund; running the cantonal calculator first shows which case applies.
Keep documentation from the start: salary statements (Lohnausweis), 3a certificates, childcare invoices, commuting evidence. Collecting them retroactively across employers is the part that turns a one-evening task into a multi-week one.