National holidays in Belgium are:
January 1st (New Year's Day),
Easter Monday (first Monday after first full moon in Spring),
May 1st (Labour Day),
Ascension Day (40 days after Easter) ,
Pentecost Monday (Monday after 50 days after Easter),
21 July (National Day),
15 August (Assumption of the Holy Virgin),
1 November (All Saints' Day),
11 November (Armistice of 1918)
December 25 (Christmas).
There a few holidays that impact the school calendar. Kids will have a week off school at the beginning of November (Vacance de Toussaint), 2 weeks of school at the end of December and beginning of January (Vacance de Noël ou Vacance d’hiver), a week off school in february (Vacance de Carnaval), 2 weeks off school usually between mid March and mid April ( Vacance de Pâques) and finally schools are closed in July and August.
Many Federal Public Services are also closed on November 2 (All Soul’s Day), November 15 (King's Day), 26 December (Boxing Day) and the applicable community holiday (Flemish: 11 July, French: 27 September, German: 15 November).
When a national holiday is on a Sunday, a lot of companies will give you a day of “compensation” . If the national holiday is on a Tuesday or Thursday a lot of companies will give an extra “bridgeday” where you do not have to work either.
https://www.belgium.be/fr/emploi/conges_et_interruption_de_carriere/jours_feries