In Dutch, the days of the week and the months start with a small letter: _maandag_, _januari_. You use _op_ before a day or a date (_op dinsdag_, _op 3 april_), and the number comes before the month. Years are said in hundreds (_negentienhonderdnegentig_) or, from 2000 on, with _tweeduizend_ plus the number.
The pattern
Inside a sentence, days and months are lowercase. Use _op_ before a day or a date: _op vrijdag_, _op 3 april_.
- Days: _maandag, dinsdag, woensdag, donderdag, vrijdag, zaterdag, zondag_.
- Months: _januari, februari, maart, april, mei, juni, juli, augustus, september, oktober, november, december_.
- A month or a year on its own takes _in_: _in mei_, _in 2025_. More in [Om, op, in: talking about time](#/lesson/time-prepositions).
- For the coming day, people often drop _op_: _Ik bel je dinsdag._
- A date is number plus month: _3 april_, said _drie april_. Formal speech sometimes uses an ordinal (a number that shows order, like third): _de derde april_.
- Years before 2000 are said in hundreds: _negentienhonderdnegentig_. From 2000 on, the usual form is _tweeduizend vierentwintig_. For recent years you also hear _twintig vierentwintig_.
Examples
| Sanne gaat op zaterdag naar de markt. | Sanne goes to the market on Saturday. |
|---|---|
| Is de supermarkt op zondag open? | Is the supermarket open on Sunday? |
| Daan is op 14 mei jarig. | It's Daan's birthday on 14 May. |
| Het is vandaag dinsdag 3 maart. | Today is Tuesday 3 March. |
| Ik heb op vrijdag 6 juni een afspraak bij de huisarts. | I have a GP appointment on Friday 6 June. |
| Yara heeft in augustus vakantie. | Yara has time off in August. |
| De burgemeester opent de nieuwe bibliotheek op de derde april. | The mayor is opening the new library on the third of April. |
| Fatima is geboren in negentienhonderdnegentig. | Fatima was born in 1990. |
| Lotte werkt hier sinds twintig tweeëntwintig. | Lotte has worked here since 2022. |
Why it works this way
Picture a wall calendar. A day or a date is one square, and you put your finger _op_ it. A month is a whole page and a year is the whole calendar: you are _in_ them. English works almost the same way (on Monday, in May), so you can mostly trust your instinct.
Remember: one square takes _op_, a whole page takes _in_.
As for the small letters: Dutch treats _maandag_ and _mei_ as ordinary nouns, like _fiets_ or _brood_. They get a capital at the start of a sentence, like any word, and in holiday names such as _Goede Vrijdag_. See [Capital letters](#/lesson/capital-letters).
Dates run from small to big: day, month, year. Dutch people write dates in figures the same way, so 3-4-2026 on a letter from the _gemeente_ means 3 April, not 4 March.
Years work like English nineteen ninety, except that Dutch keeps the word _honderd_ and writes it all as one word. In everyday writing you just use figures: _in 1990_. For building the numbers themselves, see [Numbers](#/lesson/numbers).
Watch out
- Not: _Ik werk op Maandag thuis._ Say: _Ik werk op maandag thuis._ (days are lowercase, unlike in English and German)
- Not: _De afspraak is op mei 12._ Say: _De afspraak is op 12 mei._ (the number comes before the month)
- Not: _Ik ben op juni jarig._ Say: _Ik ben in juni jarig._ (a month on its own takes _in_)
- Not: _Mijn verjaardag is in 5 mei._ Say: _Mijn verjaardag is op 5 mei._ (a date takes _op_, just like a day)
Quick check
- Choose _op_ or _in_: _Ik ga ... juli op vakantie._
- Choose _op_ or _in_: _Is de bibliotheek ... zaterdag open?_
- Fix the two mistakes: _Mijn verjaardag is op Mei 4._
- Write 1985 in words, the way people usually say it: _Sanne is geboren in ..._
Answers
- _in_: a month on its own takes _in_.
- _op_: a day takes _op_.
- _Mijn verjaardag is op 4 mei._ The month is lowercase and the number comes first.
- _negentienhonderdvijfentachtig_: years before 2000 are said in hundreds, as one word.
Use it today
Open your calendar and say three plans for this week out loud, with the day and the date, like _Op donderdag 15 oktober ga ik naar de tandarts._ Then ask a colleague: _Wanneer ben jij jarig?_