Assessment year or financial year: which year counts for Dutch tax?

The short answer

For Dutch corporate income tax the financial year counts; only without regular bookkeeping does the calendar year count (art. 7(4) Wet Vpb 1969). 'Aanslagjaar' (assessment year) is a Belgian term. An extended financial year remains one return; if the rate changes in that period, you calculate pro rata by days. A sole proprietorship in principle counts the calendar year.

Updated 30 October 2026

Key facts

Which year counts for corporate income tax?

The Wet op de vennootschapsbelasting 1969 (Dutch Corporate Income Tax Act 1969) itself says what it means by the year. Article 7(4) reads:

Year means financial year or, if the taxpayer does not keep regular books with regular annual closings, calendar year.

For a BV, NV, cooperative, foundation or association that keeps regular books, the year is therefore the financial year. That is the calendar year, unless the articles of association designate a different financial year (art. 2:10a DCC); how that works is explained under non-calendar financial year and the annual accounts. The Belastingdienst follows the financial year in the articles. Only the first, the last and an interim financial year can be longer or shorter than twelve months.

The year over which corporate income tax is calculated is thus the financial year from article 7(4), not a year that the law designates in addition. If a letter or software shows a tax year or assessment year, look at the start and end dates shown with it: that period determines which financial year is meant.

Aanslagjaar: a Belgian term

Aanslagjaar is a concept from the Belgian tax return. Wikifin, the information site of the Belgian regulator FSMA, explains that the return you file in a year always concerns the income of the preceding year: in 2026 you fill in the return with your income of 2025 (page changed on 8 January 2026). In that explanation the assessment year therefore runs one year ahead of the income year.

The Wet Vpb 1969 does not use that shift. It determines the year by the financial year itself (art. 7(4)), without moving a year. If you read Belgian explanations or work with a Belgian tool, do not add or subtract a year on your Dutch deadlines. You calculate the deadline of a Dutch return from the end of the financial year.

Extended financial year: one financial year, one return

An extended financial year is a financial year of more than twelve months. It occurs with the first financial year of a new legal entity that runs until the end of the following calendar year, with the last financial year of a legal entity that ceases to exist, and as an interim financial year when the articles change the financial year. The corporate income tax return follows the financial year (art. 7(4)): you do not file a separate return per calendar year, but one over the whole period. The taxable amount is the profit over that period.

When the return is due depends on the month in which the extended financial year ends. The Belastingdienst gives the rule on the page for foundations and associations (page changed on 23 July 2026); the corporate income tax return of a BV follows the same law and the same division:

As an example, that page gives an extended first financial year from 1 February 2023 to 30 April 2024, with a filing date before 1 October 2024. The Belastingdienst page for businesses on the corporate income tax return (read on 31 October 2026) does not mention the extended financial year; it names only the non-calendar financial year (within five months after the end) and the short financial year (if it ends in a month other than December, before 1 April of the following calendar year). An extended financial year is not a short financial year, so do not apply that 1 April rule to your extended financial year; check your date in the letter or in the message about your return. An extension of the return does not change the period for filing with the KVK (Dutch Chamber of Commerce), see CIT extension and the KVK and publication period and extension.

If you need more time, an extension of the return can be requested. The online form in Mijn Belastingdienst Zakelijk is meant for a financial year equal to the calendar year (apply before 1 June, extension until 1 November). For a deviating financial year, and thus also for an extended financial year, or if you want a longer extension, you use, according to the Belastingdienst, the paper form 'Aanvraag uitstel aangifte vennootschapsbelasting' (request for extension of the corporate income tax return), on which you substantiate your request and state until when you want an extension. The request must be received within five months after the end of the financial year (read on 31 October 2026; the page gives no date of change; source: uitstel aangifte vennootschapsbelasting). That extension applies only to the return, not to the KVK deadline.

If the extended financial year comes from a first financial year, also read a first financial year of eighteen months: it works out the length, the articles and the comparative figures.

The rate for an extended financial year

An extended financial year often runs over two calendar years. For 2023 to 2026 inclusive that makes no difference for the rate: for those four years the Belastingdienst names the same rate, 19.0% up to € 200.000 and 25.8% above. It becomes a calculation question when the rate or the bracket limit changes within the financial year. That happened on 1 January 2023: the low rate rose from 15% to 19% and the bracket limit fell from € 395.000 to € 200.000 (Rijksoverheid, the Dutch central government). For a financial year that ran across that date, article 31 Wet Vpb 1969 determines how the tax is calculated.

The Rechtbank Zeeland-West-Brabant (District Court) applied that article on 7 July 2025 to an extended first financial year from 15 February 2022 to 31 December 2023. It calculated the taxable amount once according to the rates and brackets from before the change and once according to those from after, and took from each amount the part corresponding to the number of days of the financial year falling before and after the date of change respectively. This example follows that explanation.

Case: Studio Rijn BV

Studio Rijn BV was incorporated on 1 November 2022. The articles let the first financial year run to 31 December 2023: 426 days, of which 61 in 2022 (1 November to 31 December) and 365 in 2023. The taxable amount over that whole period is € 300.000 (fictitious).

The corporate income tax for the financial year is € 61.107,98, about 20.4% of the profit. Everything under the 2023 system would have been € 63.800 and everything under the 2022 system € 45.000; the weighted result lies in between, closer to 2023 because that year counts 365 of the 426 days.

Sole proprietorship and income tax: the calendar year

A sole proprietorship has no articles of association and no legal personality of its own; the entrepreneur pays income tax on the profit. The Wet inkomstenbelasting 2001 (Dutch Income Tax Act 2001) takes the calendar year as the starting point. A different financial year is allowed only if the nature of the business justifies it. Article 3.66(1) reads:

If the nature of the business justifies this, the profit may be determined over a financial year that does not coincide with the calendar year.

Paragraph 2 says in which year that profit lands:

The profit of a financial year that does not coincide with the calendar year is regarded as profit of the calendar year in which the financial year ended.

A sole proprietorship with a financial year from 1 May 2025 to 30 April 2026 therefore reports that profit in calendar year 2026. The difference with corporate income tax is essential: for corporate income tax the year is the financial year itself, for income tax a deviating financial year is attributed to the calendar year in which it ends. Paragraph 3 deals with a financial year of more than twelve months: it is split into two parts, of which the first covers twelve months, provided the two parts end in different calendar years. Both parts then count as a separate financial year; the profit of the first part is estimated and the second part gets the rest of the profit. A long financial year for a sole proprietorship thus leads to two profit years, whereas a BV reports it as one financial year.

A partner in a vof or maatschap is himself an entrepreneur for income tax and falls under the same rule. For a BV of which you are director-major shareholder this does not apply: the BV itself pays corporate income tax, and your own income from the BV falls under income tax per calendar year.

A deviating financial year in the annual accounts themselves

A financial year of a different length also affects the annual accounts, regardless of tax. The law requires for each line item the amount of the preceding financial year, adjusted for comparability if necessary and explained (art. 2:363(5) DCC). If the previous financial year has a different length than the current one, you put two unequal periods side by side. The guideline for small legal entities advises stating in the notes the reason for the deviating length and that the figures are therefore not comparable (RJk A1.305). For a first financial year there are no comparative figures.

In Jaarrekening.io you set the financial year with a start and end date. If the period deviates from twelve months, the app proposes a text for the reason and for the comparative figures. The annual accounts contain only what you have checked and saved; the app does not guess.

For the size class, net turnover over the financial year counts. For a financial year shorter or longer than twelve months, the app tests on the higher of the actual turnover and the turnover converted to twelve months, so that the result is never lighter than either reading. The explanation of the test then states for which period and which amount this was done.

The annual accounts route of Jaarrekening.io is for legal entities under Title 9 of Book 2 DCC. For a sole proprietorship the app does not offer that route: you can create a sole proprietorship for the bookkeeping. The Taxes and Payroll modules are marked Coming soon, so you file the income tax or corporate income tax return outside the app. The first annual accounts in your account are free, for every size class; read the free annual accounts.

Common mistakes

• Setting the corporate income tax return of a BV with a non-calendar or extended financial year at 1 June anyway, although the financial year does not end on 31 December.
• Splitting an extended financial year into two returns, one per calendar year. Corporate income tax has one return per financial year.
• Applying the rate of one calendar year to the whole extended financial year although the rate or bracket limit changed within the period.
• Taking the financial year as the tax year for a sole proprietorship. For income tax the calendar year in which the financial year ends counts.
• Applying a Belgian deadline or explanation about the assessment year to Dutch rules.

Sources

• Art. 7 Wet Vpb 1969: the year is the financial year (wetten.overheid.nl, in Dutch)
• Art. 31 Wet Vpb 1969: change of rate during the financial year (wetten.overheid.nl, in Dutch)
• Rechtbank Zeeland-West-Brabant, 7 July 2025, ECLI:NL:RBZWB:2025:4288 (rechtspraak.nl, in Dutch)
• Art. 3.66 Wet IB 2001: financial year not coinciding with the calendar year (wetten.overheid.nl, in Dutch)
• Art. 3.66 Wet IB 2001, text read via inview.nl (in Dutch)
• Art. 2:10a DCC: the financial year (wetten.overheid.nl, in Dutch)
• Art. 2:363 DCC: comparative figures (wetten.overheid.nl, in Dutch)
• Belastingdienst: taxable amount and financial year (in Dutch)
• Belastingdienst: filing a corporate income tax return (in Dutch)
• Belastingdienst, Foundation and Association desk: return period and filing date (in Dutch)
• Belastingdienst: corporate income tax rates (in Dutch)
• Rijksoverheid: changes as of 2023 to the low rate in corporate income tax (in Dutch)
• Wikifin (Belgium): taxable period and assessment notice (in Dutch)

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