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German corporation tax return (KSt 1)

The Körperschaftsteuererklärung (KSt 1) declares a corporation's income for the assessment period. Together with the declaration on the separate assessment of tax bases it must be transmitted ELECTRONICALLY, in the officially prescribed dataset through the officially determined interface (§ 31(1a) KStG). For carrying out the taxation, the provisions of the Income Tax Act apply correspondingly.

Up to date for 2025 — verified on October 3, 2026Official procedure, no printed formGuide: about 60 min

This content is part of the path: Taxing a GmbH and distributing profits· Step 7 of 10· Next step: German trade tax return (GewSt 1 A)

Deadlines

Seven months after the end of the calendar year
General deadline for tax returns relating to a calendar year (§ 149(2) sentence 1 AO)
Last day of February of the second following year where a tax adviser is instructed
§ 149(3) AO — the tax office may request the return in advance in individual cases (§ 149(4) AO)
With a deviating financial year, advance payments run earlier
They must already be paid DURING the financial year that ends in the assessment period (§ 31(2) KStG)

Documents to prepare

  • ELSTER access with a certificate or an ELSTER business account
  • The corporation's tax number at the competent tax office
  • Annual accounts or the Anlage EÜR as the profit computation
  • Details for the separate assessment of tax bases
  • List of taxes to be credited and of advance payments made
  • Articles of association and shareholder details where they changed during the year
See the procedure on the official site

No form is attached to this procedure: the link leads to the official page that describes it.

What this page gives you

The guide above and the link to the official site. ActioFin does not produce any document for this page: whatever you fill in or file is done on the official medium.

Who this applies to

  • Corporations, in particular the GmbH and the UG (haftungsbeschränkt), as well as cooperatives
  • Associations and other corporations under private law, including tax-privileged ones — for charitable, benevolent and church associations ELSTER points to a guide from North Rhine-Westphalia that can be used nationwide
  • Corporations whose financial year DIFFERS from the calendar year, for which § 31(2) KStG lays down its own rule on advance payments
  • Sole traders and partnerships are NOT concerned: they declare their result for income tax, not for corporation tax

Worked example

Nordlicht Verpackungen GmbH, with a financial year from 1 July to 30 June

Its 2024/2025 financial year ends on 30 June 2025, that is within the 2025 assessment period — so it declares that year in the KSt 1 for 2025. For advance payments the special rule of § 31(2) KStG applies: they must already be paid during that financial year, that is between July 2024 and June 2025, and not only in calendar year 2025. If the assessment produces a corporation tax of 18,750.63 euros, that amount is rounded under § 31(1) sentence 2 KStG to full euros in the company's favour, so to 18,750 euros. Alongside the KSt 1 the company transmits the declaration on the separate assessment of tax bases — § 31(1a) KStG names both in the same breath, and both must be filed electronically.

How to fill it in, step by step

  1. Establish which assessment period applies — with a deviating financial year it is the period in which the financial year ENDS.
  2. Determine the corporation's income under the Corporation Tax Act and, where that Act provides nothing else, under the Income Tax Act (§ 31(1) sentence 1 KStG).
  3. Sign in to Mein ELSTER and select „Körperschaftsteuererklärung (KSt 1)“ and the calendar year.
  4. Complete the KSt 1 with the details of the company, its income and the taxes to be credited.
  5. Prepare the declaration on the separate assessment of tax bases: § 31(1a) KStG requires it alongside the tax return, not instead of it.
  6. Transmit the profit computation with it — the content of the balance sheet and profit and loss account as an officially prescribed data record (E-Bilanz, § 5b EStG), not as an attached document, or the Anlage EÜR, depending on how profit is determined.
  7. Transmit both declarations with authentication through the officially determined interface.

Good to know

  • The individual corporation tax amounts are rounded to full euros IN FAVOUR of the taxpayer on assessment (§ 31(1) sentence 2 KStG) — the rounding is therefore never to the company's detriment.
  • For carrying out the taxation, the provisions of the Income Tax Act apply CORRESPONDINGLY unless the Corporation Tax Act provides otherwise (§ 31(1) sentence 1 KStG). That covers crediting, payment and refund as well as the surtaxes.
  • § 37b EStG — the flat-rate taxation of benefits in kind — applies correspondingly (§ 31(1) sentence 3 KStG).
  • In hardship cases the tax authority may on request waive electronic transmission; the declarations are then filed on the official form and signed by hand by the LEGAL REPRESENTATIVE (§ 31(1a) sentence 2 KStG).
  • Corporation tax is not the company's only income tax: the trade profit is declared separately, and the municipality levies trade tax on it.

Common mistakes

  • Transmitting only the KSt 1. § 31(1a) sentence 1 KStG names the corporation tax return AND the declaration on the separate assessment of tax bases — both must be filed electronically.
  • Choosing the wrong assessment period with a deviating financial year. What counts is the period in which the financial year ENDS (§ 31(2) KStG speaks of the financial year ending in the assessment period).
  • With a deviating financial year, making the advance payments only in the assessment year. They must already be paid DURING the financial year (§ 31(2) KStG).
  • Having the paper version signed by an authorised agent. § 31(1a) sentence 2 KStG requires the handwritten signature of the LEGAL REPRESENTATIVE.
  • Assuming a charitable association has no filing duty. ELSTER expressly lists the corporation tax return for associations too and provides a guide for them.

Frequently asked questions

Must the return be filed electronically?

Yes. § 31(1a) sentence 1 KStG requires transmission in the officially prescribed dataset through the officially determined interface, for the corporation tax return as for the declaration on the separate assessment. Only on request may the tax authority waive this to avoid undue hardship.

Which assessment period applies where the financial year is not the calendar year?

The period in which the financial year ends. § 31(2) KStG builds on that and at the same time provides that advance payments must already be made during that financial year.

By when must the return be filed?

At the latest seven months after the end of the calendar year (§ 149(2) sentence 1 AO); where a tax adviser is instructed, by the last day of February of the second calendar year following the assessment period (§ 149(3) AO).

Is the assessed tax rounded?

Yes, and in the taxpayer's favour: the individual corporation tax amounts arising on assessment are each to be rounded to full euro amounts (§ 31(1) sentence 2 KStG).

Does this return also apply to a GmbH & Co. KG?

Not to the KG itself: a partnership does not declare its result for corporation tax. The general partner GmbH, by contrast, is a corporation and files its own corporation tax return.

Go further

Compute the related amounts

Understand this form: the related course

Related forms

Official sources

Read in German

Guide and document provided for information purposes only; they do not constitute personalised legal or tax advice. Check the recipient organisation's requirements and consult a professional if needed.