TAX Deadline

If you mean income tax, the deadline is today (15 July). It was extended for two weeks.

https://eservices.minfin.fgov.be/taxonweb/app/citizen/public/taxbox/home.do

See the bottom of the page:

"La date limite pour rentrer votre déclaration en ligne est le 15 juillet 2019 (impôt des personnes physiques)."

As CM notes above, it is TODAY.

Your alternative is to have an accountant do it, you have to inform the tax authorities before the end of AUgust, and the accountant has until November to file the return.