Understanding Swiss Withholding Tax (Quellensteuer/Impôt à la source) – A 2025 Update

Foreign employees in Switzerland often encounter a different income tax system known as withholding tax (“Quellensteuer” in German, impôt à la source in French). This system can be confusing for new residents, especially with recent reforms. This article explains what Swiss withholding tax is, who it applies to, how and when it transitions into the regular tax system, and how one can optimize or reclaim taxes under this regime. We also summarize the important 2021 reform and any updates since, drawing on official guidance and expert commentary.

What Is Swiss Withholding Tax and How Does It Differ from Ordinary Tax?

Swiss withholding tax is a tax on income that is deducted directly from your salary by your employer, rather than being paid through the standard annual tax return process. In practice, your employer withholds a portion of your gross wage each month and remits it to the cantonal tax authorities. This payment covers federal, cantonal, and communal income taxes.

For employees, this typically means that taxes are paid automatically throughout the year, with minimal intervention or effort required. In most cases, no annual tax filing is necessary, as the tax is settled at source on an ongoing basis.

This system mainly applies to foreign residents in Switzerland who do not hold a C permit (permanent residence). In contrast, Swiss citizens and permanent residents (C permit holders) typically pay taxes via the standard procedure: they receive provisional tax invoices based on income estimates and make payments throughout the year. Early in the following year, they file a yearly tax return. After the tax authorities assess the submitted return, a final tax bill is issued, which may result in either an additional payment or a refund.

The withholding tax system is designed to simplify tax collection for non-permanent residents and to ensure compliance by collecting tax “at the source” (i.e. from the salary). Unlike the ordinary system, withholding tax uses predefined tax tariffs and does not use the exact same tax brackets or detailed deductions as a normal tax assessment. In other words, it’s a simplified taxation intended to approximate the individual’s income tax liability.

Who Has to Pay Withholding Tax in Switzerland?

All foreign workers residing in Switzerland on a non-permanent basis are generally subject to tax at source. This includes holders of B permits (residence permit) and L permits (short-term residence), as well as most other foreign employees living in Switzerland who have not yet obtained a C permit.

However, there are important exceptions: if a foreign resident is married to a Swiss citizen or to a C permit holder, or if they themselves obtain a C permit, they are exempt from withholding tax and instead follow the ordinary tax process. In fact, B or L permit holders married to a Swiss or C-permit spouse are treated like residents for tax purposes and must file regular tax returns rather than having tax deducted from salary.

Switzerland also applies withholding tax to certain non-residents who earn Swiss-source income. For example, cross-border commuters (frontier workers who live in a neighboring country but work in Switzerland), weekly residents, as well as foreign performers (lecturers, athletes, artists, etc. when paid in Switzerland) are typically taxed at source on their Swiss earnings. The exact treatment of cross-border workers depends on bilateral tax treaties. For instance, many French-resident frontaliers working in Geneva or Vaud are taxed primarily in France (and exempt from Swiss source tax) if they return home daily and meet the treaty conditions. If those conditions aren’t met (e.g. not returning home regularly or missing the residency attestation), then Swiss withholding tax is applied by the employer.

Other taxpayers – namely Swiss nationals and foreigners with a C permit or equivalent status – are not subject to the withholding tax. They must file an annual tax return and are taxed via the standard assessment procedure instead.

When Does Withholding Tax Liability End?

Your obligation to pay tax at source in Switzerland ends once you gain a more permanent status or integration into the normal tax system. The transition triggers are straightforward:

• obtaining a C permit (settlement permit)

• becoming a Swiss citizen

• marrying a Swiss citizen (or a C permit holder)

In these cases, you switch to ordinary taxation as a Swiss resident.

Importantly, the change doesn’t wait until a new tax year – it takes effect immediately upon status change. Official guidance notes that “the tax at source is no longer due from the month following the granting of the settlement permit (or Swiss nationality) or the marriage”. In other words, in the month after you receive your C permit or marry a Swiss, your employer should stop withholding tax. From that point forward, you’ll be taxed via the normal process (filing a return for that year’s income). Any source tax already deducted in that calendar year is credited toward your eventual ordinary tax bill, without interest.

For example, if you received a C permit in July, the tax for January–June that was withheld will be credited against the tax calculated in your ordinary assessment for the whole year. You will then file a tax return for that year (and future years), as a newly ordinary-taxed person. Essentially, achieving permanent residency or similar status concludes your withholding tax obligation and integrates you into the standard tax system mid-year.

Do Withholding Taxpayers Ever Need to File a Tax Return?

For many people taxed at source, the monthly withholding is final – no further filing is required. However, there are notable cases when a tax return must (or can) be filed even if you’re on withholding tax:

High Income

If a person subject to withholding tax earns above a certain threshold (CHF 120,000 per year in all cantons), they are legally required to file an annual tax return. (Before 2021, some cantons had higher thresholds – for instance, Geneva only required a return if income exceeded CHF 500,000, but this has since been aligned to CHF 120k.) When this threshold is exceeded, the taxpayer undergoes a “subsequent ordinary assessment”: the year’s income is assessed like a regular taxpayer’s would be, and the already-withheld tax is credited against the final tax due. It is important to note that if a married couple is taxed at source, the CHF 120k threshold applies to either of their Swiss-source incomes; if one spouse exceeds this amount, it necessitates a tax return for the couple. It is worth noting that once someone has been pulled into an ordinary tax assessment due to high income, they will remain on ordinary tax assessments in future years (until they exit the tax system entirely) even if their income falls below the threshold later.

Additional Income or Assets

If a withholding tax paying individual has other sources of income not subject to withholding, or owns significant taxable assets, a tax return may be required. Examples include:

• income from self-employment or freelance work

• rental income

• investment earnings

• pensions

• sizable wealth in Switzerland

In such cases, Swiss law mandates a mandatory ordinary tax assessment so that those additional incomes/wealth are properly taxed. Many cantons enforce this with specific thresholds. For instance, in Vaud any taxable wealth or non-wage income triggers a return; Geneva explicitly sets a wealth threshold (approx. CHF 83,000 in assets for singles, CHF 166,000 for married couples) above which a return is required. Other cantons have their own criteria; some publish minimum thresholds for secondary income or asset values, while others assess it on a case-by-case basis. While the Federal Tax Administration attempted to harmonize this, cantonal differences still remain in practice.

Voluntary Filing for Deductions

Since a major reform in 2021 (detailed later), foreign residents taxed at source who earn below CHF 120,000 and don’t meet any of the above criteria may choose to file a tax return voluntarily to claim additional deductions or a potential refund. This is sometimes referred to as requesting a “voluntary retroactive ordinary assessment” (Freiwillige nachträgliche ordentliche Veranlagung in German, or NOV). Common situations include people who made large pension contributions (pillar 2 buy-ins or pillar 3a payments), have high deductible expenses, or other factors that would lower their tax if accounted for fully. By default, someone under the CHF 120k threshold with only a salary does not need to file any return – the withheld tax is considered final. But if they want to reclaim overpaid tax (due to deductions not included in the withholding calculation), they can opt in to an ordinary tax filing to recalculate their liability.

However, keep in mind that opting for a voluntary ordinary assessment can sometimes result in a higher tax bill than the source tax – because the withholding rates are averaged, some taxpayers (especially in high-tax municipalities) actually pay slightly less at source than they would under a full assessment.

Common deductible items that source-taxed individuals can only benefit from by filing a return include:

• pillar 3a contributions

• pension fund buy-ins

• alimony paid

• childcare costs

• large medical bills

• educational expenses

If you have none of these and only standard income, the hassle of an ordinary filing might not be worthwhile. But if you do, know that the system provides a mechanism to reclaim overpaid tax.

Reclaiming Overpaid Tax and Deductions for Withholding Taxpayers

One downside of the withholding tax system is that it’s somewhat “one-size-fits-all” – the rates include only standard allowances (like a basic work expense allowance and a general deduction for insurance, etc.) but do not account for individualized deductions.

For example, if you contribute to a Pillar 3a retirement account, make voluntary pension fund buy-ins, pay a lot of childcare or alimony, or have high medical expenses, the withholding tax has no way of adjusting month-by-month for these situations. This can lead to “overpayment” relative to your true tax liability if those deductions were considered.

To address this, taxpayers have options to claim refunds or adjustments:

Tax Return / Ordinary Assessment

Filing a full tax return for the year is now the primary way to claim additional deductions if you are taxed at source. Starting with the 2021 reform, employees cannot simply file a short correction form to deduct things like Pillar 3a or pension buy-ins from their taxable income. Instead, they must request a recalculation via an ordinary tax filing to get credit for those deductions. This involves notifying the canton (by March 31) and then submitting a complete tax return listing your income, assets, and deductions. The tax office will then compute your tax as if you were an ordinary taxpayer, apply all eligible deductions, and compare that to what was withheld. If the withholding was higher than the recalculated tax, you get a refund; if it was lower, you would have to pay the difference.

Withholding Tax Correction (Rectification)

Apart from big-ticket deductions, there is still a process to correct errors in the withholding itself. If, for example, the wrong tariff or rate was applied (say, your employer didn’t account for the fact you have children, or they taxed you as single when you married during the year), you can request a tariff correction from the cantonal tax office by the end of March of the following year. This is essentially an adjustment of the withheld amount without a full tax return, used to fix incorrect assumptions (marital status, number of dependents, days worked outside Switzerland, etc.). Prior to 2021, one could also use this rectification process to claim certain deductions (like declaring pillar 3a contributions), but as of 2021 that is no longer allowed for most deductions. Now, the correction process is generally limited to factual errors in withholding, while any elective deductions must go through an ordinary assessment.

Quasi-resident Deductions for Cross-border Workers

If you live outside Switzerland but are taxed at source on Swiss income, you can potentially reclaim overpaid tax by qualifying as a “quasi-resident.” This means 90% or more of your worldwide income is taxable in Switzerland (for example, a cross-border commuter who earns almost all income in CH). In such cases, you are entitled to be treated like a Swiss resident for tax purposes, meaning you can file a return to claim deductions and be taxed at ordinary rates rather than just the flat withholding.

How Rates Are Determined: Tariff Categories and Cantonal Differences

Unlike a single unified tax rate, Swiss withholding tax is calculated based on tariff tables that vary by canton and personal situation. Each canton sets its own withholding rates reflecting that canton’s income tax levels (including communal taxes). This means the percentage withheld from your salary will differ depending on where you live (or work, for non-residents), sometimes significantly. The federal government publishes annual withholding rate tables for each canton to standardize employer calculations, but the underlying rates are tied to cantonal tax policy.

Tariff Categories

Personal status factors play a major role. Withholding tax schedules are divided into tariff categories (typically labeled A, B, C, etc.) which account for your marital status and dependents:

Tariff A

For single, unmarried individuals without children or other dependents in the household. This is the standard rate for a single person. (Sub-entries A0, A1, A2… indicate number of children if any – though if children are present in the same household, often a different tariff like H may apply, see below.)

Tariff B

For married single-earner households (married couples where only one spouse earns an income). This tariff assumes the other spouse has no earnings and provides a more favorable rate (with married deductions) for one breadwinner. It can apply with or without children (e.g., B0 no kids, B1 one kid, etc. as sub-categories). The key is that the spouse isn’t employed or has only minimal income.

Tariff C

For married double-earner couples (both spouses are working). This tariff is less lenient than B, because it assumes two incomes contribute to the household. Both with and without children variants exist (C0, C1, C2, etc.). Even if the spouse’s income is earned abroad, the guidance is to treat the situation as a double-earner (Tariff C) for withholding purposes, to fairly reflect the higher combined economic capacity.

Tariff D

Typically used for secondary income jobs or side earnings. For example, if you have a second job, the second employer might apply Tariff D (which withholds at a higher rate on that income) since your primary allowance is used up by the first job. Tariff D ensures additional wages are taxed as if on top of your main income.

Tariff H

For single parents (single, divorced, or widowed individuals living with and supporting children). This category provides for the parental deduction and lower rates recognizing the dependents, even though the person is not married. (Some cantons use “H” or similar letters for this scenario, granting benefits akin to married status due to child support responsibilities.)

These categories are applied by employers based on the personal data you provide (marital status, spouse’s employment, number of kids, etc.). It’s crucial to notify your employer of any status change (marriage, divorce, birth of a child, spouse starting a job, etc.) so they can adjust the tariff and withhold the correct amount. The withholding tax rates already incorporate certain flat deductions depending on the tariff – for example, the rates for married people are lower to account for marital deductions, and rates for those with children factor in child allowances. This is why, if you are taxed at source, you cannot separately claim those common deductions; they’re included in the tariff.

Cantonal differences

Switzerland’s tax system is highly decentralized, with each canton and municipality levying their own taxes at varying rates. This leads to significant differences in tax burdens depending on where a person lives. Withholding tax (Quellensteuer), which is directly deducted from a salary, is especially impacted by these regional variations.

Switzerland also employs a progressive tax system, meaning that tax rates increase with income. However, the applicable rate is influenced not only by income level, but also by personal circumstances such as marital status, number of children, religious affiliation, and how household income is distributed. As a result, two households with identical total incomes may be taxed at very different rates.

For example, in Zurich, a married couple with a single income of CHF 200,000 might face a withholding tax rate of 13.7%, while a dual-income couple earning the same combined amount could pay only 9.7%. The difference arises from the use of distinct withholding tax tariffs for single-earner and dual-earner households.

Each canton has its own tariff tables. A single person with no children earning CHF 6,000 per month might see substantially different withholding tax rates depending on the canton. While the federal portion of the tax is uniform nationwide, cantonal and municipal taxes can vary widely. In low-tax cantons like Zug or Schwyz, the withholding rate may be relatively modest, while in high-tax cantons like Geneva or Vaud, the rate could be double or more for the same income.

Withholding tax is intended to approximate the final tax liability under the ordinary taxation system. Therefore, if a canton imposes higher taxes on residents overall, the corresponding withholding tax will be higher as well. Conversely, in cantons known for low tax rates, withholding tax is generally lighter.

Examples of Tax Differences by Canton and Family Situation

To illustrate how withholding tax can vary, consider the following examples (using simplified rates):

Single Person with Income of 140,000 / 200,000 CHF

Take for example of a single individual with no children and no religious affiliation earning CHF 140,000 per year. The tax rate this person faces can range widely from one canton to another:

Zurich: 12.5%

Zug: 7.1%

Lausanne: 17.8%

Now, if the same person earns CHF 200,000 annually, the rates increase due to tax progression:

Zurich: 17.2%

Zug: 10.8%

Lausanne: 22.5%

💍 Marital Status: ❌ (Single)
👶 Children: ❌ (None)
💰 Annual Salary: CHF 140,000 / 120,000
⛪ Religious Affiliation: ❌ (None)
📍 Residence: 🇨🇭 Zürich or Zug or Lausanne

This highlights how both location and income level directly affect the effective tax burden. Zug, known for its business-friendly and low-tax environment, offers significantly lower rates, while cities like Lausanne impose much steeper progressive taxes. As a result, the choice of residence can lead to annual tax differences of several thousand francs.

Married Couple with Single Income of 200,000 / 300,000 CHF

For married couples with a single income, tax rates are generally lower than for single individuals, as marital status often qualifies for a more favorable tariff. At an income of CHF 200,000, the applicable rates are:

Zurich: 13.7%

Zug: 7.0%

Lausanne: 17.6%

At an income of CHF 300,000, tax progression results in higher applicable rates:

Zurich: 17.6%

Zug: 11.8%

Lausanne: 23.4%

💍 Marital Status: Married
👶 Children: ❌ (None)
💰 Annual Salary: Single Income of CHF 200,000 / 300,000
⛪ Religious Affiliation: ❌ (None)
📍 Residence: 🇨🇭 Zürich or Zug or Lausanne

As the graphic show here, for married couples with a single income, the applicable tax rate is generally lower than for single individuals, thanks to more favorable tariff structures. This difference is evident when comparing a married couple earning CHF 200,000 in Zurich (13.7%) to a single person with the same income in the same canton (17.2%). The 3.5 percentage point gap stems entirely from household status, despite the identical income—highlighting how the tariff system incorporates standard deductions based on family configuration.

Remarkably, this married couple’s rate at CHF 200,000 is nearly the same as that of a single person earning just CHF 140,000 in Zurich (12.5%), despite the significantly higher income. This underscores the substantial impact of the marital tariff in reducing the effective tax burden.

However, tax progression becomes more pronounced at higher income levels. At CHF 300,000, rates increase across the board: 17.6% in Zurich, 11.8% in Zug, and 23.4% in Lausanne. Yet even at this level, the married couple’s tax rate is comparable to that of a single person earning CHF 200,000—particularly in Zurich and Lausanne—once again demonstrating how the tariff system adjusts for household structure.

Nonetheless, location remains a key factor. In Zug, a married couple earning CHF 300,000 pays just 11.8%, while the same household in Lausanne faces a steep 23.4%. The interplay of progressive taxation and cantonal tax policies leads to sharp regional disparities—showing that both family status and place of residence play a decisive role in determining overall tax liability.

Married Couple with Dual Incomes of 200,000 / 300,000 CHF

When both spouses earn an income—a scenario that is increasingly common—the tax treatment changes again. For a combined household income of CHF 200,000, the applicable rates are:

Zurich: 9.7%

Zug: 4.5%

Lausanne: 13.7%

At a combined household income of CHF 300,000, the applicable tax rates adjust accordingly:

Zurich: 12.8%

Zug: 6.9%

Lausanne: 17.2%

💍 Marital Status: Married
👶 Children: ❌ (None)
💰 Annual Salary: Dual Income of CHF 200,000 / 300,000
⛪ Religious Affiliation: ❌ (None)
📍 Residence: 🇨🇭 Zürich or Zug or Lausanne

These graphics showcase that a dual-income household benefits from one of the most favorable tax tariffs in the Swiss system. Precisely, a couple earning a combined CHF 200,000 (CHF 100,000 each) pays just 9.7% in Zurich, compared to 13.7% for a single-earner couple with the same total income—a significant reduction purely due to the way the income is split.

At a combined income of CHF 300,000, a dual-income household in Zurich (with a 50/50 split) continues to benefit, facing a tax rate of only 12.8%, while a single-earner couple at the same income level is taxed at 17.6%. This demonstrates how Switzerland’s tariff structure actively favors income splitting, resulting in substantially lower tax liabilities.

Once again, canton choice plays a critical role. A dual-income household earning CHF 300,000 pays just 6.9% in Zug, while the same household in Lausanne would be taxed at 17.2%. These stark contrasts highlight how both income distribution within a household and canton of residence significantly influence the effective tax burden.

The 2021 Withholding Tax Reform: What Changed?

January 1, 2021 marked the implementation of a comprehensive reform of the Swiss withholding tax law on employment income. This reform was driven by a need for equal treatment and harmonization. Under the old system, some foreign workers complained (and even took cases to European courts) that they couldn’t access the same deductions as ordinary taxpayers, violating bilateral agreements on equal treatment. The reform aimed to address these issues and to standardize the source tax procedures across all cantons. Here are the key changes that came into effect in 2021:

Standardized Criteria for Ordinary Taxation

The threshold for mandatory ordinary taxation was fixed at CHF 120,000 nationwide, forcing high-earning source taxpayers to be treated like everyone else after that point. (As noted, Geneva had to lower its threshold from a much higher level to comply.) Additionally, having any significant non-wage income or wealth now triggers ordinary taxation in all cantons, though each canton can set small thresholds for what “significant” means. This ensures that two people in different cantons with similar situations will both be required to file if, say, they have a side business or large investments, rather than it depending on local practice.

End of Tariff Correction for Most Deductions

Prior to 2021, a person taxed at source could file a tariff correction form to adjust their taxable income for certain deductions (notably pension buy-ins and Pillar 3a contributions) without doing a full tax return. This was a convenient shortcut. The reform abolished that possibility: “as of 1 January 2021, employees can no longer use a withholding tax tariff correction form to claim deductions from pension buy-ins and Pillar 3a contributions”. Now, any tax benefit from those deductions requires a full tax return. The rationale was to align with equal treatment – giving those deductions only through ordinary assessment, same as a Swiss taxpayer would claim them. Practically, this means foreign employees have to decide by year-end if it’s worth making extra pension contributions, since they will only get the tax relief if they commit to filing a return.

Uniform Deadlines and Procedure

The reform set a single deadline of March 31 of the following year for both mandatory filings and voluntary requests nationwide. It also clarified that if you leave Switzerland, you must request any assessment before you deregister (or else lose the chance). This harmonization removes cantonal discrepancies in deadlines or processes. Additionally, employers were given clear guidelines: for example, in some cantons like Zurich, from 2021 the employer must determine the correct tariff code themselves (no longer receiving it from the authorities) and the employee can appeal or request an ordinary assessment if they disagree.

Cross-border Commuters and Quasi-residency

The reform addressed the treatment of non-resident weekly commuters by making the 90% rule a strict prerequisite to file a return. In the past, not all cantons enforced the 90% “quasi-resident” test rigorously – some allowed cross-border workers to file for corrections more liberally. As of 2021, an international weekly resident (living abroad, working in Switzerland) can only claim additional deductions via a tax return if they meet the 90% Swiss income test or specific tax treaty provisions. If they don’t, the source tax withheld is final. This change was in response to European Court of Justice cases that Switzerland needed to treat EU resident workers equitably if most of their income is taxed in Switzerland. Now, the law attempts to codify when a non-resident can be treated like a Swiss resident for tax purposes. However, the practical implementation of this is still evolving – further guidance or court decisions are expected to clarify the finer points of who exactly can benefit from quasi-resident status.

Employer Obligations and “Economic Employer” Concept

From 2021, the law also clarified that any employer with a Swiss presence who economically employs a person is responsible for withholding tax. This was aimed at situations like international assignments, where formally a foreign entity pays the salary. The circular No. 45 introduced the idea of an “economic employer” in Switzerland – if a Swiss entity bears the cost or risk of the employee, it must withhold Swiss tax, even if the contractual employer is abroad. This prevents companies from avoiding Swiss withholding by paying through foreign payrolls, and it harmonized cantonal practice on this point.

Developments Since 2021: Implementation and Updates

Since the reform’s rollout, Swiss authorities and cantons have been fine-tuning its implementation. By 2022 and 2023, all cantons adjusted their regulations to align with federal law, though some nuances remain:

Cantonal Thresholds for Non-wage Income

As noted, not every canton initially had clear thresholds for when a withholding tax payer must file due to other income/assets. This lack of uniformity caused some uncertainty. In response, many cantons have published guidance. For example, Zurich set thresholds (additional income over CHF 3,000 or wealth over CHF 80,000 triggers an ordinary assessment), Geneva specified its wealth thresholds as mentioned earlier, and others like Bern or Basel communicated their policies internally. The trend is toward more transparency so taxpayers know when they must file.

Awareness of Voluntary Filing Option

Since 2021 was the first year foreigners below CHF 120k could proactively request ordinary taxation, not everyone was aware of it. Over the past couple of years, cantons have improved communication. Some cantonal tax websites (Fribourg, Vaud, Zurich, etc.) explicitly mention that a request must be made each year by March 31 if a taxpayer wants a retrospective ordinary assessment for additional deductions. If you miss the request, you can’t later claim those deductions. By now, large employers and HR departments are also more accustomed to reminding source-taxed employees of the March 31 deadline if they wish to file a return.

Handling of Mid-year Permit Changes

With more mobility (many foreigners obtaining C permits or marrying Swiss each year), tax offices have clarified how to handle split-year situations. The Vaud tax administration (for example) explicitly notes that once a person switches to ordinary taxation mid-year (due to a C permit, etc.), the withholding for the rest of that year stops and the taxes for the whole year are settled via the ordinary return, crediting the first part’s withheld tax. Any overpayment is refunded and any underpayment billed. This was always the case, but the guidance is now clearer, stressing that the change happens immediately from the next month.

Court Rulings and Interpretations

Some aspects of the new law have been subject to legal interpretation. One area is the 90% quasi-resident rule for cross-border workers. Because the law (Art. 99a of Federal Act on Direct Federal Tax) also includes clauses for cases where a taxpayer’s situation is “comparable to a resident” or when a treaty requires allowing deductions, there have been questions on how strictly to interpret the 90% test. As of 2023, tax advisors note that the authorities have provided little additional guidance on these clauses, and some cases may end up in tax court to set precedents. It remains to be seen how generous or strict the application will be for cross-border commuters who, say, earn slightly under 90% in Switzerland or have unique circumstances. Early cases in 2021-2022 (including a Federal Supreme Court case in April 2021, 2C_60/2020, involving Geneva) dealt with previous law but set some principles on equal treatment for EU resident taxpayers. We expect further rulings to refine the quasi-residency criteria under the new regime.

Continued Compliance Focus

The reform also underscored that employers and taxpayers must stay compliant. If a taxpayer is required to file a return (due to high income or other factors) and fails to do so, tax authorities can issue an assessment and potentially fines or penalties for tax evasion. In one 2023 case, a taxpayer in Geneva faced back taxes and fines for 2008–2013 related to withholding tax mis-declarations. Such cases highlight that even under withholding tax, one cannot ignore tax obligations (e.g., not reporting additional income). The systems between payroll and tax offices are tightening, and cantons share data, so any omission (like undeclared income) can lead to a Nachsteuer (retroactive tax) plus penalties.