How withholding tax actually works for B permit holders
Withholding tax is deducted by your employer from your monthly gross salary and paid directly to the cantonal tax authority. The rate is applied to your gross income and does not account for any personal deductions you may be entitled to claim. The important implication is that the withholding tax system calculates your estimated tax liability as if you had zero deductions. If you have Pillar 3a contributions, commuting costs, or work-related expenses, the withholding rate will almost certainly overestimate your actual tax liability for the year.
The supplementary return: the mechanism most people do not use
B permit holders with salaries below CHF 120,000 per year are not required to file a full tax return. However, they have the right to file a supplementary return to claim deductions and recover the resulting overpayment. Deductions available include Pillar 3a contributions, commuting costs, work-related expenses, health insurance premiums, and home office costs. The supplementary return must be requested voluntarily. The canton does not notify you that you are eligible.
The CHF 120,000 threshold: mandatory vs optional filing
Once your gross salary from a single employer in Switzerland exceeds CHF 120,000 per year, you are automatically required to file a full ordinary tax return regardless of your permit type. The withholding tax paid during the year is treated as a prepayment toward your final tax liability. Above CHF 120,000, filing a full return is not optional.
Wrong tax codes: the silent overpayment
Your withholding tax deduction is calculated using a code that reflects your civil status. An incorrect code means your employer is withholding at the wrong rate. The correction can be made by notifying your employer to update the code with the cantonal tax authority. The overpaid tax from prior months can typically be recovered through the annual process.