An amended (supplementary) tax return is filed after the deadline for the regular return, once you discover your tax should have been different. In both Slovakia and the Czech Republic, filing is mandatory when the tax should have been higher and voluntary when it should have been lower, but the deadlines, penalties and interest differ, so a business operating in both countries needs to understand each system.
When must you file an amended return?
In both countries the trigger is the same: you must act once you find that your tax should have been higher than declared. Slovakia (Act No. 563/2009 Coll., the Tax Code) and the Czech Republic (Act No. 280/2009 Coll., the Tax Code) both set the deadline at the end of the month following the month in which you discovered the error, and both require you to pay the difference within that same period.
So if a Slovak or Czech company spots unreported income in September, the amended return and the extra payment are due by 31 October. The date of discovery is stated in the form and starts the clock. For a company active in both markets, our overview of Slovak tax advisory for companies explains how we handle such cross-border obligations.
When is filing voluntary?
If the tax should have been lower, filing is a right, not a duty, in both countries, and the state will not refund an overpayment on its own. A practical difference appears here: in the Czech Republic the one-month deadline does not apply to returns lowering the tax, and you are limited only by the general deadline for assessing tax. Slovakia works similarly, capping voluntary filings by the statute of limitations rather than by a monthly deadline.
What is the difference between an amended and a corrective return?
Both systems distinguish a corrective return, filed before the regular deadline expires and free of any penalty, from an amended (supplementary) return, filed after the deadline. The logic is identical: corrective before the term, amended after it. Only the amended return can carry financial consequences.
How long is the filing window?
This is where the two regimes part ways. In Slovakia the basic period for assessing tax is five years from the end of the year in which the regular return was due, extended to seven years where a tax loss is carried forward. In the Czech Republic the basic period is shorter, only three years, but it can be extended, suspended and interrupted, with an absolute ceiling of ten years. In neither country does simply waiting make the problem disappear.
Penalties: where the systems really differ?
The biggest practical gap is in penalties. Slovakia charges a penalty on the tax difference under Section 155 of its Tax Code even when you file voluntarily: at least 3 % per year if you file yourself, rising to a minimum of 7 % if the difference emerges during an audit and 10 % if the tax authority assesses it. On top of that comes late-payment interest of at least 15 % per year under Section 156, capped at four years.
The Czech Republic is more forgiving to honest taxpayers. Its 20 % penalty under Section 251 applies only when the tax is assessed by the authority, typically after an audit; file voluntarily and you pay no penalty at all. You still owe late-payment interest under Section 252, set at the Czech National Bank repo rate plus 8 percentage points, which reached 11.75 % per year in the second half of 2026. In short, a voluntary Czech filing avoids the penalty entirely, whereas a Slovak one does not.
How do you file in each country?
In both cases you use the standard return form, mark it as supplementary (dodatočné in Slovak, dodatečné in Czech), and state the date you discovered the reason together with the difference against the last known tax. Legal entities and VAT payers file electronically through the respective tax portals, and the tax difference is payable within the filing deadline. The overriding rule in both jurisdictions is the same: the sooner and more voluntarily you file, the less you pay.
Do you run a company in Slovakia, the Czech Republic, or both, and need to correct an already filed tax return? We will review it and prepare the amended return so that you pay only what is strictly necessary.
FAQ
What is the deadline for filing an amended tax return?
In both Slovakia and the Czech Republic, if the tax should have been higher, you must file the amended return by the end of the month following the month of discovery and pay the difference within the same period. For returns lowering the tax, no monthly deadline applies and you are limited only by the period for assessing tax.
Do I pay a penalty if I file voluntarily?
It depends on the country. In Slovakia you pay a penalty on the tax difference even when filing voluntarily, at a minimum of 3 % per year, plus 15 % annual late-payment interest. In the Czech Republic a voluntary filing carries no penalty; you owe only late-payment interest, which was 11.75 % per year in the second half of 2026.
What is the difference between a corrective and an amended return?
A corrective return is filed before the regular deadline expires and carries no penalty. An amended (supplementary) return is filed after the deadline, once you discover the figures were wrong. Only the amended return can trigger penalties or interest.