The term Nieuwjaar means ‘new year.’ If you want to wish people in the Netherlands ‘Happy new year,’ you say ‘Gelukkig Nieuwjaar!’
The new year did not always start on January 1st. During the French occupation (1795-1815), the year started on 22 September. During the Middle Ages, some people used the Christmas style while others used the Eastern style calendar, named after the day that was considered the first day of the year. The Eastern calendar is particularly cumbersome since the timing of Eastern changes each year with the moon cycle so the time between two celebrations of Eastern can be significantly more or less than 365 days, leading to duplicate or missing dates.