---
title: "Swiss Source Tax (Quellensteuer): Cantonal Withholding, NOV Opt-In, CHF 120,000 Threshold"
country: switzerland
service: "source-tax-quellensteuer-and-cantonal-tax-domicile"
category: finance
difficulty: complex
estimated_time: "Monthly withholding is automatic via employer payroll. Where filed, the optional or mandatory ordinary-assessment return is typically 3-8 hours to compile and 3-12 months for the cantonal administration to issue the final decision."
cost_range: "Source tax is a statutory withholding (a percentage of gross wage; rate varies by canton, family status, and income bracket), not an administrative fee. There is no application fee for the optional ordinary-assessment opt-in; canton-specific extension fees on mandatory filings are typically CHF 20-40."
last_verified: 2026-05-18
canonical: https://publicservices.guide/switzerland/canton-tax-domicile-and-source-tax-quellensteuer/
status: current
confidence: low
tags:
  - quellensteuer
  - "source-tax"
  - "cantonal-tax"
  - "nov-tou"
  - "chf-120000-threshold"
  - "cross-border-worker"
  - "quasi-resident"
  - "pillar-3a"
sources:
  - https://www.estv.admin.ch/estv/de/home/direkte-bundessteuer/dbst-quellensteuer.html
  - https://www.estv.admin.ch/de/quellensteuer
  - https://www.fedlex.admin.ch/eli/cc/1991/1184_1184_1184/de
  - https://www.zh.ch/de/steuern-finanzen/steuern/quellensteuer.html
  - https://www.ge.ch/impot-source
  - https://www.vd.ch/etat-droit-finances/impots/impot-a-la-source-pour-les-employeurs-et-les-personnes-imposees-a-la-source
  - https://taxinfo.sv.fin.be.ch/taxinfo/display/taxinfo/Nachtr%C3%A4gliche+ordentliche+Veranlagung
  - https://www.ag.ch/media/kanton-aargau/dfr/dokumente/steuern/quellensteuer/quellensteuer-arbeitnehmende/1-045-d-faq-kreisschreiben-45-d.pdf
---

# Swiss Source Tax (Quellensteuer): Cantonal Withholding, NOV Opt-In, CHF 120,000 Threshold

**Country:** 🇨🇭 Switzerland  
**Last verified:** 2026-05-18  
**Estimated time:** Monthly withholding is automatic via employer payroll. Where filed, the optional or mandatory ordinary-assessment return is typically 3-8 hours to compile and 3-12 months for the cantonal administration to issue the final decision.  
**Cost:** Source tax is a statutory withholding (a percentage of gross wage; rate varies by canton, family status, and income bracket), not an administrative fee. There is no application fee for the optional ordinary-assessment opt-in; canton-specific extension fees on mandatory filings are typically CHF 20-40.

## Required documents

- **Source-tax registration declaration** *(Quellensteuer-Anmeldung / déclaration pour l'impôt à la source / dichiarazione per imposta alla fonte)*
  - Purpose: Establishes civil status, dependent children, religious denomination, spouse's employment status, and other Swiss income. Sets the tariff code applied from the first monthly wage.
  - Filed by: Employee signs; employer transmits to the cantonal tax administration within 8 days of hire. Changes reported within 14 days; corrected tariff applies from the first day of the following month.
- **Residence permit** *(Aufenthaltsbewilligung B / L / Ci or Grenzgängerbewilligung G)*
  - Purpose: Establishes that source tax applies. Permit type on the card triggers source-tax registration; C-permit holders are not source-taxed.
  - Required form: Original card for in-person verification at hire; certified copy where the employer onboards remotely.
- **Passport or national identity document**
  - Purpose: Federal and cantonal identity verification at hire and at any change of registration.
  - Required form: Original or certified copy.
- **Annual wage certificate** *(Lohnausweis / certificat de salaire / certificato di salario)*
  - Purpose: Documents gross annual wage, source tax withheld, Pillar 2 contributions, and other employment items. Primary evidence in any ordinary-assessment return.
  - Issued by: Employer, no later than 28 February of the year following the tax year.
- **Cantonal tax return package** *(Steuererklärung / déclaration d'impôt / dichiarazione d'imposta)*
  - Required when: Mandatory NOV / TOU triggered (CHF 120,000 wage threshold or substantial non-source-taxed income or wealth), OR opt-in request filed, OR resident has acquired a C permit or married a Swiss / C-permit holder.
  - Filed via: Cantonal e-tax portal — ZHprivateTax, e-Démarches, VaudTax, TaxMe-Online — or paper return. Lists worldwide income and wealth.
- **Optional opt-in request form** *(Antrag auf nachträgliche ordentliche Veranlagung / demande de taxation ordinaire ultérieure)*
  - Required when: Resident wishes to claim Pillar 3a, Pillar 2 buy-in, training, or other personal deductions and gross annual wage did not reach CHF 120,000.
  - Deadline: 31 March of the year following the tax year. Non-extendable; late requests are rejected. Irrevocable: ordinary assessment continues every subsequent year of source-tax liability.
- **Pillar 3a deposit certificate** *(Bescheinigung 3a / attestation 3a / attestazione 3a)*
  - Purpose: Evidence of Pillar 3a contributions for the tax year, deductible only via ordinary assessment.
  - Issued by: The 3a provider (bank or insurer) by mid-February of the year following the contribution year.
- **Pillar 2 voluntary buy-in confirmation** *(Einkaufsbestätigung Pensionskasse / attestation de rachat de prévoyance)*
  - Purpose: Evidence of a voluntary buy-in into the second pillar; deductible against ordinary assessment, not source tax directly.
  - Issued by: The pension fund on request after the buy-in is paid in.
- **Health-insurance premium certificate** *(KVG-Prämienbestätigung / attestation de primes LAMal)*
  - Purpose: Documents mandatory-health-insurance (Krankenkasse) premiums paid. Cantonal returns allow a lump-sum or actual-cost deduction.
  - Issued by: The health insurer, in January or February of the year following the premium year.
- **Worldwide-income evidence (cross-border workers)**
  - Required when: Quasi-resident ordinary assessment (Art. 99a DBG) requires evidence of at least 90% worldwide gross family income from Swiss-source income.
  - Acceptable forms: Residence-country tax assessment, wage or income confirmation, or certified income statement from the residence-country tax authority.

## Costs

- **Optional opt-in request (NOV / TOU on request, Art. 89a DBG):** 0 CHF — No application fee. Filed by 31 March of the year following the tax year; non-extendable and non-restorable. The cantonal tax return is then filed via the cantonal e-tax portal.
- **Cantonal extension request on mandatory NOV / TOU return (optional):** 20–40 CHF — Canton-specific. Where the return is filed under mandatory NOV / TOU (Art. 89 DBG, e.g. after the CHF 120,000 threshold has been reached), an extension is routinely granted on request — typical extended deadlines are 30 September or 30 November. The fee is at the cantonal administration's discretion; CHF 20-40 is the typical published range. The cantonal source-tax page lists the exact fee.
- **Cantonal e-tax portal access:** 0 CHF — No fee. ZHprivateTax (Zürich), e-Démarches (Geneva), VaudTax (Vaud), TaxMe-Online (Bern), and equivalent portals in other cantons are free to use.

## Steps

### 1. Employer registers the new hire for source tax

- The employer (legally the Schuldner der steuerbaren Leistung — debtor of the taxable benefit) applies source tax to the wage of every foreign-national employee without a C permit, every cross-border worker, and every weekly resident
- Within 8 days of hire, the employer registers the source-taxed employee with the cantonal tax administration of the employee's canton of residence (or workplace, for non-resident cross-border or weekly workers)
- Registration is via the cantonal source-tax employer portal (e-DPI for Vaud, eQuellensteuer for Zürich, online portal for Geneva, source-tax portal for Bern) or via certified payroll software using the Swissdec ELM standard
- The cantonal administration confirms the applicable tariff code (e.g. A0N for a single person with no dependents and no church-tax membership; B1Y for a married single-earner with one child and church-tax membership)

> **Tip:** The employee signs the registration declaration capturing civil status, dependent children with date of birth, religious denomination, spouse's employment status, and any other Swiss income. The resulting tariff code applies from the first monthly wage.

### 2. Employer applies the tariff and remits monthly

- Each monthly payroll cycle, the employer applies the applicable tariff (codes A / B / C / D / E / G / H / L / M / N / P / Q / R, with the Y or N church-tax suffix)
- The tariff is computed on annualised gross wage divided by twelve, so a one-off bonus is taxed as if it recurred all year
- The employer remits withheld source tax to the cantonal tax administration within 30 days of month-end and files the monthly Lohnsumme / liste récapitulative declaration
- The cantonal administration pays the employer a collection commission (Bezugsprovision) of typically 1-3% of withheld source tax

> **Tip:** Source tax is final for residents whose gross annual wage stays below CHF 120,000 and who have no other taxable income or wealth above cantonal de-minimis thresholds, with no optional opt-in filed.

### 3. Report civil-status changes to the employer within 14 days

- Report marriage, birth of a child, separation, divorce, denomination change, or spouse taking up / leaving employment to the employer within 14 days
- The employer transmits the change via the source-tax employer portal
- The corrected tariff applies from the first day of the month following the change

> **Tip:** Example: an employee who marries on 15 June and has a first child on 20 September moves from tariff A0 to tariff B0 / C0 from 1 July and to tariff B1 / C1 from 1 October.

> **If this fails:** If the change is not reported, the cantonal administration will eventually learn of it through municipal civil-status records and apply a retroactive tariff adjustment.

### 4. Receive the annual wage certificate by 28 February

- The employer issues the wage certificate (Lohnausweis / certificat de salaire / certificato di salario) no later than 28 February of the year following the tax year
- The certificate shows gross annual wage, source tax withheld, Pillar 2 contributions, and other employment items
- Keep the certificate as primary evidence for any ordinary-assessment return

### 5. File mandatory ordinary assessment if the CHF 120,000 threshold is met

_Applies when: If gross annual employment income reached CHF 120,000, OR if substantial non-source-taxed income or wealth exists above cantonal de-minimis thresholds_

- The cantonal tax administration issues an invitation to file the standard cantonal tax return for the tax year
- File the return via the cantonal e-tax portal (ZHprivateTax, e-Démarches, VaudTax, TaxMe-Online, equivalent in other cantons) by 31 March of the year following the tax year
- Request an extension before 31 March if needed — extensions are routinely granted to 30 September or 30 November against a small fee, typically CHF 20-40
- List worldwide income and wealth — same return filed by every ordinary-assessment resident in the canton
- The cantonal administration credits source tax already withheld against the ordinary-tax burden and issues a Veranlagungsverfügung — additional bill or refund

> **Tip:** Once mandatory ordinary assessment is triggered, the procedure continues automatically every subsequent year of source-tax liability — the CHF 120,000 threshold is not re-tested each year.

> **If this fails:** If the return is not filed by the cantonal deadline, the administration issues an ex-officio assessment based on its own estimate of taxable income — generally less favourable.

### 6. Opt in to ordinary assessment if you want to claim deductions

_Applies when: If gross annual wage was below CHF 120,000 AND you wish to claim Pillar 3a, Pillar 2 voluntary buy-in, training, childcare, or other personal deductions against source tax_

- File the optional opt-in request (Antrag auf nachträgliche ordentliche Veranlagung / demande de taxation ordinaire ultérieure) with the cantonal tax administration of your canton of residence by 31 March of the year following the tax year
- The deadline is non-extendable and non-restorable; late requests are rejected
- Complete the standard cantonal tax return via the cantonal e-tax portal
- The cantonal administration recomputes total tax under ordinary assessment, credits source tax already withheld, and issues a Veranlagungsverfügung

> **Tip:** Calculate whether the year-one refund exceeds the cumulative tax-burden swing over the years source-tax liability is expected to continue before opting in. The opt-in is irrevocable.

> **If this fails:** If gross annual wage falls well below CHF 120,000 in a later year with no special deductions, ordinary assessment may produce a higher tax burden than source tax would have. You cannot reverse the opt-in.

### 7. File the quasi-resident opt-in if you are a cross-border worker

_Applies when: If you are a cross-border worker or weekly resident AND at least 90% of worldwide gross family income is Swiss-source_

- File the quasi-resident opt-in with the cantonal tax administration of your canton of work by 31 March of the year following the tax year
- Include worldwide-income evidence — residence-country tax assessment, wage or income confirmation, or a certified income statement from the residence-country tax authority
- The cantonal administration verifies the 90% threshold and, if satisfied, issues a Veranlagungsverfügung
- Unlike the Art. 89a opt-in for residents, the quasi-resident opt-in is filed annually — quasi-residency is re-tested each tax year

> **Tip:** Cross-border workers with substantial foreign rental, self-employment, or capital income may fall below the 90% threshold and be ineligible in that year.

### 8. Handle a cross-canton move

_Applies when: If you move from one canton to another during the tax year_

- Deregister at the commune of origin (Abmeldung) and register at the commune of destination (Anmeldung) within 14 days
- The new commune notifies the new cantonal tax administration of your domicile change
- Notify your employer of the new address; the employer transmits the change via the source-tax employer portal
- From the first day of the month following the move, the new canton's source-tax tariff applies
- For ordinary assessment (where applicable), the canton of residence on 31 December is the canton of assessment for the entire year

> **If this fails:** If the move is not registered, the cantonal administrations will eventually reconcile via inter-cantonal data exchange and apply a retroactive tariff adjustment.

### 9. Receive the final assessment and pay or receive the refund

- The cantonal administration issues a Veranlagungsverfügung showing the computed tax, source tax credited, and the resulting balance
- Refunds are paid to the bank account nominated on the return — typically a Swiss IBAN
- Additional bills are payable within 30 days of the decision becoming final; an instalment plan is generally available on request
- Challenge the decision via Einsprache / réclamation within 30 days of receipt

> **Tip:** Processing time from filing to Veranlagungsverfügung is typically 3-12 months, varying by canton and by complexity of the return.

## FAQ

### I just got my B permit and started a job in Zürich. Do I need to do anything for source tax?

No initial action by you. The employer registers you with the cantonal tax administration of Zürich within 8 days of hire and applies the appropriate source-tax tariff to each monthly wage. You sign a short declaration form (Quellensteuer-Anmeldung) capturing civil status, dependent children, religious denomination, and any other Swiss income; the employer transmits it to the canton.

### Will I get a tax bill at year-end?

Generally no. For a source-taxed resident whose gross annual wage stays below CHF 120,000 and who has no other taxable income or wealth above the cantonal de-minimis thresholds, source tax is the final tax for that year — no annual return is filed. If gross annual wage reaches CHF 120,000, you enter mandatory ordinary assessment (Art. 89 DBG): file the standard cantonal tax return by 31 March of the following year (extension routinely granted) and the cantonal administration credits the source tax already withheld against the ordinary-tax burden — producing either an additional bill or a refund.

### I earn under CHF 120,000 — can I claim my Pillar 3a deduction against source tax?

Only by filing the optional opt-in (Art. 89a DBG; nachträgliche ordentliche Veranlagung auf Antrag / taxation ordinaire ultérieure sur demande) by 31 March of the year following the tax year. The opt-in is irrevocable: in every subsequent year of source-tax liability the cantonal administration carries out ordinary assessment automatically. Calculate carefully whether the year-one Pillar 3a refund exceeds the cumulative tax-burden swing over subsequent years before opting in. The 2021 reform abolished the previous tariff-correction route (Tarifkorrektur) that allowed a Pillar 3a deduction without committing to ordinary assessment.

### What happens if I forget to declare a marriage to my employer?

You face a retroactive tariff adjustment when the cantonal administration learns of the marriage — typically via municipal records, since civil-status changes are reported by communes automatically. The adjustment can produce a refund (single-earner married tariff B is generally lower than single-person tariff A) or an additional bill (dual-earner married tariff C can be higher in some configurations). Report civil-status changes to your employer within 14 days of the event.

### I moved from Zürich to Geneva in May. Which canton taxes me?

For source tax: Zürich's tariff applies through April; Geneva's tariff applies from May (first day of the month after the move). For ordinary assessment (if you are subject to mandatory NOV / TOU or have filed the optional opt-in), the canton in which you reside on 31 December of the tax year is the canton of assessment for the entire year. In this example, Geneva is the canton of assessment, and you file a single return with Geneva covering the full year's worldwide income and wealth.

### I got my C permit in August. Am I still source-taxed?

Source-tax liability ends at the end of August. From 1 September you enter ordinary assessment and file the standard cantonal tax return for the full tax year. The cantonal administration credits the source tax withheld from January through August against the year's ordinary-tax burden. The mid-year transition does not by itself trigger the irrevocability of the Art. 89a opt-in.

### I am a cross-border worker from Germany. Am I source-taxed in Switzerland?

Yes — your Swiss employer applies source tax at the cross-border-worker tariff defined by the Germany-Switzerland double-tax treaty (typically tariff code L for daily commuters). If at least 90% of your worldwide gross family income is taxed in Switzerland, you can apply for quasi-resident ordinary assessment (Art. 99a DBG) by 31 March of the year following the tax year. The quasi-resident opt-in is filed annually — unlike the Art. 89a opt-in for residents, it is not automatic in subsequent years.

### Once I file the optional opt-in, can I switch back to plain source tax later?

No. The Art. 89a opt-in is irrevocable for as long as source-tax liability lasts. Ordinary assessment is then carried out automatically every subsequent year. Liability ends only when source-tax liability itself ends — typically by acquiring a C permit, marrying a Swiss citizen or C-permit holder, or leaving Switzerland. This is the principal trap of the 2021 reform: weigh the year-one refund against the cumulative effect over the years source-tax liability is expected to continue.

### My partner and I live together but are not married. Does that change my source tax?

No. For source-tax purposes, registered partnership (Eingetragene Partnerschaft / partenariat enregistré, since 2007, including same-sex partnership) is treated like marriage and triggers tariff codes B (single-earner) or C (dual-earner). Unmarried cohabitation does not — each cohabitant remains on their own tariff (A for single without children, H for single-parent).

### I am a quasi-resident and filed the Art. 99a opt-in last year — do I file again this year?

Yes. Quasi-resident ordinary assessment under Art. 99a DBG is filed annually by 31 March of the year following each tax year. Unlike the Art. 89a opt-in for residents (irrevocable and automatic from year two), quasi-residency is re-tested each year against the 90% worldwide-income threshold. If your Swiss-source share drops below 90% in any year, you cannot file the quasi-resident return for that year.

### I work part-time for two Swiss employers. How is source tax calculated?

Each employer applies source tax separately on the wage it pays. Because each employer only sees its own bracket, cumulative withholding can fall short of the marginal rate on total wage. To avoid systematic under-withholding, declare the secondary job to the primary employer so tariff D (Nebenerwerb / activité accessoire) is applied to the secondary income, or file the optional Art. 89a opt-in to true up at year-end.

### I am moving to Switzerland mid-year. How is the CHF 120,000 threshold tested?

Monthly gross wage is annualised by twelve months to determine whether the CHF 120,000 threshold is reached, regardless of the calendar months actually worked in the tax year. Example: starting work on 1 October at a gross monthly wage of CHF 11,000 annualises to CHF 132,000, triggering mandatory NOV / TOU even though actual three-month earnings are only CHF 33,000. Once triggered by annualisation, ordinary assessment continues automatically every subsequent year.

## Local tips

- Verify your permit type before assuming source tax applies. B (residence), L (short-stay), Ci (intergovernmental-organisation family member), and G (cross-border) permits trigger source tax for foreign nationals; C (settlement) permits and Swiss citizenship do not. Foreign nationals married to a Swiss citizen or to a C-permit holder also enter ordinary assessment regardless of the foreign-national spouse's own permit class.
- Report civil-status changes (marriage, birth of a child, separation, divorce, denomination change, spouse employment change) to your employer within 14 days. The corrected tariff code applies from the first day of the month following the change.
- Think twice before filing the optional opt-in (Art. 89a DBG) just to claim a Pillar 3a deduction. Once filed, the opt-in is irrevocable: you remain in ordinary assessment every subsequent year while source-tax liability lasts. In a later year with no special deductions, ordinary tax may exceed the source tax withheld and produce a bill rather than a refund.
- The optional opt-in deadline is 31 March of the year following the tax year. Non-extendable and non-restorable — late requests are rejected. Pillar 3a, Pillar 2 buy-ins, training costs, and childcare costs above the cantonal lump-sum are lost for that year if the deadline is missed.
- If you move between cantons during the year, the new canton's tariff applies from the first day of the month following the move. For an ordinary-assessment return (where filed), the canton of residence on 31 December is the canton of assessment for the entire year.

## Sources

- [Eidgenössische Steuerverwaltung (ESTV) — federal source-tax landing page](https://www.estv.admin.ch/estv/de/home/direkte-bundessteuer/dbst-quellensteuer.html) — accessed 2026-05-18 — _T1_ — Source tax is directly deducted from income. Applies to foreign nationals without a C permit who are tax-resident in Switzerland, to cross-border workers, and to weekly residents. The 31 March deadline for the optional Art. 89a DBG opt-in is non-extendable. Pillar 3a deduction is only available via subsequent ordinary assessment.
- [Eidgenössische Steuerverwaltung (ESTV) — 2026 cantonal source-tax tariff release](https://www.estv.admin.ch/de/quellensteuer) — accessed 2026-05-18 — _T1_ — 2026 cantonal source-tax tariff files released on 4 March 2026 for entry into force 1 January 2026. Corrective re-release for canton Aargau adjusted contribution-limit cap for tariff codes L / M / N / Q from CHF 1,000,000 to CHF 99,999. Standardised median monthly wage rose from CHF 5,775 (2025) to CHF 5,875 (2026); assumed Pillar 2 (BVG) deduction rose from 6.0% to 6.5%.
- [Bundeskanzlei — Fedlex federal statute portal (DBG, SR 642.11)](https://www.fedlex.admin.ch/eli/cc/1991/1184_1184_1184/de) — accessed 2026-05-18 — _T1_ — Articles 83-100 of the Federal Act on Direct Federal Tax (DBG; SR 642.11) govern source tax. Art. 89 sets mandatory subsequent ordinary assessment at CHF 120,000 gross annual wage or substantial non-source-taxed income or wealth. Art. 89a establishes the optional opt-in by 31 March, irrevocable once filed. Art. 99a establishes the quasi-resident opt-in for cross-border workers / weekly residents at the 90% Swiss-source threshold. Art. 107 designates the canton of residence (or workplace for non-residents) as the competent tax authority.
- [Kantonales Steueramt Zürich — canton Zürich source-tax landing page](https://www.zh.ch/de/steuern-finanzen/steuern/quellensteuer.html) — accessed 2026-05-18 — _T1_ — Revised source-tax act applies from 1 January 2021. Tariff codes A / B / C / D / E / G / H / L / M / N / P / Q / R with Y / N church-tax suffix apply in canton Zürich. Federal Kreisschreiben Nr. 45 cited as legal basis. Substantial non-source-taxed income or wealth triggers mandatory ordinary assessment alongside the CHF 120,000 threshold.
- [Administration fiscale cantonale Genève — canton Geneva source-tax landing page](https://www.ge.ch/impot-source) — accessed 2026-05-18 — _T1_ — Civil-status changes must be reported within 14 days; corrected tariff applies from the first day of the following month. Monthly source-tax tariff is calculated on annualised gross wage divided by twelve. Canton Geneva tariff codes: A0-A5, B0-B5, C0-C5, H, G, A1-A5 (alimony), D (AVS reimbursement for departing non-treaty-country residents).
- [Administration cantonale des impôts Vaud — canton Vaud source-tax employer and resident page](https://www.vd.ch/etat-droit-finances/impots/impot-a-la-source-pour-les-employeurs-et-les-personnes-imposees-a-la-source) — accessed 2026-05-18 — _T1_ — Conseil d'État decision of 26 November 2025 embedded a cumulative 5% reduction of basic cantonal tax in the 2026 source-tax barèmes (one percentage point over the 4% applied in 2025), with a stated plan to reach 7% cumulative in 2027. Reflected in most tariff codes; capital-payment scales (I / J / K) and the fixed-rate special scale (E) are out of scope. Employer remits withheld source tax within 30 days of month-end.
- [Steuerverwaltung Kanton Bern — TaxInfo subsequent ordinary assessment reference](https://taxinfo.sv.fin.be.ch/taxinfo/display/taxinfo/Nachtr%C3%A4gliche+ordentliche+Veranlagung) — accessed 2026-05-18 — _T1_ — CHF 120,000 mandatory ordinary-assessment threshold (Art. 89 DBG) applies to annualised gross annual wage; mid-year employment annualises monthly gross wage over twelve months. Quasi-resident ordinary assessment (Art. 99a DBG) requires at least 90% of worldwide gross family income to be Swiss-source. For cross-canton moves, canton of residence on 31 December is the canton of assessment for the entire year; new canton's source-tax tariff applies from the first day of the month following the move. From 1 January 2026, source-tax remittances for Moutier route to canton Jura.
- [Steueramt Kanton Aargau — FAQ Kreisschreiben Nr. 45](https://www.ag.ch/media/kanton-aargau/dfr/dokumente/steuern/quellensteuer/quellensteuer-arbeitnehmende/1-045-d-faq-kreisschreiben-45-d.pdf) — accessed 2026-05-18 — _T1_ — Kreisschreiben Nr. 45 binding on all 26 cantons from 1 January 2021. Art. 89a opt-in is irrevocable: ordinary assessment continues every subsequent year of source-tax liability. Art. 99a quasi-resident opt-in requires at least 90% Swiss-source family income and is filed annually — quasi-residency is re-tested each tax year.

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Canonical: https://publicservices.guide/switzerland/canton-tax-domicile-and-source-tax-quellensteuer/