As a rule, the social security contributions must be in the account no later than the last day of the quarter in question.
If your debt has not been settled by the final payment date, you will owe an increase of 3% on the unpaid part. As long as you do not pay your contribution in full, a new increase of 3% will be added every quarter, on top of the unpaid part. In addition, a one-off increase of 7% will be charged if you still have outstanding contributions on 31 December.

Exception
There is only one exception to this rule: Starters who are affiliated in time are given an extra quarter of time for the first two quarters of affiliation to pay the provisional social contribution.