Haven’t filed your 2025 tax return yet? How to make the most of the summer deadlines

Deadlines are cantonal – an overview

There is no uniform filing deadline across Switzerland: each canton regulates submission and extensions itself. The ordinary deadline is typically 31 March, in some cantons the end of April. Extensions are possible almost everywhere – usually online in a few clicks and generally free of charge. The maximum deadlines, however, differ considerably: many cantons extend to 30 September as standard, in some cases to 30 November upon a justified request. In the canton of Zurich, for example, an extension already granted until 30 September can be extended again until the end of November from August onwards; in Solothurn, the free extension is only available until the end of July, after which a fee-based request becomes necessary. The crucial point: the extension must be requested before the current deadline expires – a retrospective request does not cure the delay. So check now which deadline is actually running for you in your canton.

Reminder, fine, discretionary assessment: the escalation ladder

What happens if the deadline passes? First, the tax administration sends a reminder, which depending on the canton carries a fee of around 40 to 60 francs. If the reminder deadline also lapses, a second, chargeable reminder usually follows – and after that, things become unpleasant: the authority estimates your income and assets at its due discretion. Experience shows that such discretionary assessments rarely work out in the taxpayer’s favour, as the estimates are deliberately on the high side. Your options to challenge them are limited: an objection against a discretionary assessment is only admissible if the missing tax return is submitted in full and the assessment can be shown to be obviously incorrect. In addition, procedural fines may be imposed, which can rise sharply for repeated breaches. In short: every step up the escalation ladder costs money and nerves – and all of them are avoidable.

Requesting an extension the right way

In most cantons, the path to an extension is refreshingly simple: via the tax administration’s online portal, the deadline can be extended in a few minutes using the reference number of your tax return. Three points matter. First: keep the confirmation – it is your proof in case of any dispute. Second: note the new deadline in your calendar, because a further extension is not possible in every canton. Third: think of any additional obligations, for instance if you are liable to tax in several cantons – because of a holiday flat or a property outside your canton of residence, for example. And do not forget: the extension only postpones the filing, not the interest calculation. If you expect an additional payment, you are often better off adjusting the provisional invoice or making a voluntary instalment payment to avoid compensatory interest.

Self-employed persons and complex situations: being early pays off

For the self-employed, owners of several properties or people with securities portfolios, the tax return is more than filling in forms: financial statements, depreciation, maintenance costs and pension contributions need to be properly prepared. Those who wait until autumn run into the fiduciary sector’s peak season – and risk leaving no time for optimisation. Yet this is precisely where the potential lies: pension fund purchases, pillar 3a contributions, the right timing for property maintenance or the separation of private and business costs cannot be corrected retroactively, but they can be planned for the current year. Our tip: use the quieter summer weeks. With a complete set of documents, the tax return is prepared quickly – and you head into autumn with a clean slate.