Every entry below is the rule as Netherlands publishes it. It is a reference, not a calendar: where a deadline runs from something only you know, this page says so instead of showing a date.
This is the rule as published by the registry, checked against the primary source on the date shown. It is not your filing date. Where a deadline runs from incorporation, from a fiscal year the company itself elects, or from an event only you know about, no date can be derived here at all — the figure you see is the formula, not the answer. Extensions, transitional regimes and entity-specific exemptions are not reflected. Confirm with the registry before you rely on a date.
The Dutch financial year (boekjaar) is normally the calendar year, but the company's articles of association may set a different one, so the financial year is a date the user must supply rather than a statutory constant. KVK publishes the annual-accounts deadline as a period counted from the end of the financial year, not as a calendar date: the accounts must be filed «binnen 12 maanden na afloop van het boekjaar» (within 12 months after the end of the financial year). That twelve-month figure is the outer statutory limit; in the ordinary chain the board prepares the accounts within five months, shareholders may extend that by up to five months in special circumstances, then have two months to adopt them, and the accounts must be filed within eight days of adoption. KVK states the combined effect for a bv whose shareholders are all directors: «je deponeert binnen tien maanden en acht dagen na afloop van het boekjaar». Because the financial year end is user-supplied and the deadline is a period rather than a calendar date, no filing deadline is shown here as a calendar number. The corporate income tax return runs on its own clock (five months after the end of the financial year / 1 June for a calendar-year company); the VAT return runs from the calendar tax period, independent of the financial year.