How to check your Swiss tax return for errors (even one a fiduciary filed)

Key takeaways

• You can check a Swiss tax return for errors in about ten minutes by comparing it against your own documents. You do not need any tax expertise.
• Under Swiss law you are responsible for the return, even when a fiduciary (TreuhänderTreuhänderFiduciary / tax preparerFRfiduciaireITfiduciarioSomeone who prepares returns for a fee. The title is not legally protected in Switzerland, and you remain liable for the return regardless of who filled it in.Where you see itOn page 1 of the Zurich return, in the representative block, where the field is labelled Treuhänder-ID.Open in the glossary →, a professional tax preparer) filled it in. The law asks you to complete it truthfully and completely and to sign it yourself (DBGDBGThe federal income tax actFRLIFDBundesgesetz über die direkte Bundessteuer: the act that governs federal income tax for the whole country. Almost every federal rule a guide cites comes from here, which is why the abbreviation appears so often beside an article number.Where you see itIn citations, as DBG Art. 33 or similar. French and Italian sources call the same act LIFD.Open in the glossary → Art. 124 para 2).
• Three errors cover most of it: a document from the wrong tax year, income already inside the salary certificate counted a second time, and a deduction that was there last year and is gone this year.
• Check before it is filed where you can. The tax office can open a supplementary-tax procedure up to 10 years after the tax period, and set the amount for up to 15.
• Once the assessment has arrived you have 30 days to object, and an objection re-opens the whole year in both directions.

Who is responsible for a Swiss tax return

The signature (or electronic submission) on a Swiss tax return is yours, whoever prepared it. The Federal Direct Tax Act (DBG) Art. 124 para 2 puts the duty on the taxpayer: complete the return truthfully and completely, sign it personally, file it on time. Art. 126 para 1 adds that you must do everything needed to make a correct assessment possible. Neither article mentions your preparer.

If an error understates your income, the tax office can collect the missing tax with interest (DBG Art. 151). It can open that procedure for up to 10 years after the end of the tax period, and set the amount for up to 15 years (DBG Art. 152 paras 1 and 3). If an error runs the other way, overstating your income or dropping a deduction, you simply pay more than you owed and nothing in the assessment points it out.

Whether to hire one at all is a separate question: do you need a Treuhänder?

Errors to check for

These examples show what to compare when checking a return against your documents. They are useful checks whether you prepared the return yourself or someone prepared it for you.

A document from the wrong tax year. A salary certificate, an insurance-premium statement, or a pillar 3a (Säule 3aSäule 3aPillar 3aFRpilier 3a (prévoyance individuelle liée)ITpilastro 3a (previdenza individuale vincolata)Tied private retirement savings. What you pay in during the year comes straight off your taxable income, up to a legal maximum.Where you see itYour provider sends a contribution certificate in January.Open in the glossary →, tax-favoured private pension) attestation from one year gets used in another year's filing. The number looks reasonable, so nothing flags it.

Income counted twice. Some benefits are paid through your employer and are already inside your salary certificate (LohnausweisLohnausweisSalary certificateFRcertificat de salaireITcertificato di salarioYour employer’s annual statement of your salary, benefits and deductions. You normally receive one from each employer and use it to enter employment income in the return.Where you see itSent by your employer in January or February.Open in the glossary →). Maternity pay and employer-routed sick pay are common examples. Entered again as a separate income line, the same money is taxed twice.

A deduction that vanished since last year. A commute, an insurance premium, a 3a contribution claimed last year is missing this year with no reason. Deductions do not disappear on their own; a missing one usually means it was overlooked.

How to check a prepared return

Check three things against your own documents before a prepared return is filed, or when the assessment arrives. This takes about ten minutes.

1. Year on every document. Check the salary certificate (Lohnausweis), the insurance-premium statement and the pillar 3a attestation. Does each one show the tax year being filed?
2. Income counted once. Benefits already inside your salary certificate (maternity pay, employer-routed sick pay) must not appear again as a separate income line.
3. Last year versus this year. Put the two returns side by side and check the commute, insurance and 3a. Any deduction that existed last year and is gone this year needs a reason, not an assumption.

If any of the three does not match, ask before the return is filed. A question costs nothing; a supplementary-tax procedure years later costs money and time.

• 1The tax year on every documentCheck itSalary certificate, insurance-premium statement, pillar 3a attestation: each must show the year being filed
• 2Income counted onceCheck itMaternity pay and employer-routed sick pay are already inside the salary certificate; a second income line taxes the same money twice
• 3Last year beside this yearCheck itA deduction that existed last year and is gone this year needs a reason, not an assumption

You are responsible for the return whoever prepared it. A preparer works only from the documents you handed over.

You found something. Now what?

Which route you take depends on where the return is in the process.

Where you are	Route	What it is
Filed, not yet assessed	Correction	Most cantons accept a corrected return at any point while the assessment is not yet legally final; several, Zurich among them, take it by simply submitting online again.
Assessment arrived, within 30 days	Objection (Einsprache). See reading your assessment	The formal route (DBG Art. 132 para 1). It re-opens the assessment in both directions: the tax office may re-set every factor and, after hearing you, decide against you (DBG Art. 135 para 1). Expect the whole year to be looked at again.
Assessment final, income was undeclared	Voluntary disclosure (straflose Selbstanzeige)	Tell the tax office before it finds out. The first time, the penalty is waived; any later disclosure only cuts the fine to one fifth of the evaded tax (DBG Art. 175 paras 3 and 4). The back tax and interest are owed either way.

If income or an account was left out entirely, that is the voluntary-disclosure conversation, and it is worth taking advice before you write the letter.

Common questions

Am I liable for a mistake my fiduciary made?

Yes. DBG Art. 124 para 2 puts the duty to file a truthful and complete return on the taxpayer, not on whoever typed it. A preparer's error can still lead to supplementary tax (NachsteuerNachsteuerSupplementary taxFRrappel d'impôtITricupero d'impostaTax the canton can collect later when income or wealth was not declared, going back up to ten years after the tax period, plus interest.Where you see itOnly if the tax office opens proceedings. It is not part of a normal filing.Open in the glossary →) assessed against you.

How far back can the tax office go?

For direct federal tax, the right to open a supplementary-tax procedure lapses 10 years after the end of the tax period, and the right to set the amount lapses after 15 years (DBG Art. 152 paras 1 and 3). The amount owed carries interest. Cantonal and communal taxes follow the same two limits (StHGStHGThe cantonal tax harmonisation actFRLHIDITLAIDSteuerharmonisierungsgesetz: the act that tells all 26 cantons which taxes they must levy and how the rules must be shaped. It sets the frame; each canton still fixes its own rates and many of its own deduction ceilings inside it.Where you see itIn citations as StHG Art. 13 or similar, usually beside the DBG article covering the same point federally.Open in the glossary → Art. 53 paras 2 and 3).

Sources

The sources below support the tax figures and rules discussed in this guide. Follow the links to check the original guidance and its scope.

1. DBG (SR 642.11) Art. 124 para 2 and Art. 126 para 1 — the taxpayer must complete the return truthfully and completely, sign it personally, and enable a correct assessment — fedlex.admin.ch
2. DBG Art. 151 (supplementary tax) and Art. 152 paras 1 and 3 (10 years to open the procedure, 15 years to set the amount) — fedlex.admin.ch
3. DBG Art. 132 para 1 (objection within 30 days) and Art. 135 para 1 (the tax office may re-set every factor and rule against you) — fedlex.admin.ch
4. DBG Art. 147 para 2 and Art. 148 (reconsideration: excluded where you could have raised the point earlier; 90 days from discovery) — fedlex.admin.ch
5. DBG Art. 175 paras 3 and 4 (first voluntary disclosure penalty-free; any later one reduced to one fifth of the evaded tax) — fedlex.admin.ch
6. StHG (SR 642.14) Art. 48 (objection, 30 days, decided in both directions) and Art. 53 paras 2 and 3 (the same 10- and 15-year limits for cantonal and communal taxes) — fedlex.admin.ch
7. Canton Zurich — tax return for private individuals: corrections may be submitted at any time while the assessment is not yet legally final — zh.ch