Русско-англо-русский юридический словарь

Consumer Focus says individuals quite rightly assume that once a judgment is awarded by the court, full and prompt payment should follow – but this is frequently not the case. "Those who don't receive payment find themselves initiating enforcement proceedings, which cost money, but, more worryingly, often fail to recover compensation," it says, warning of the "high and growing number" of enforcement cases. (The Guardian)

Let us assume that a supplier has sent you goods giving you 30 days credit. Till the 30 days are up, the amount is outstanding but not overdue. After 30 days the amount is outstanding and is overdue.

‘Overdue’ is sometimes called ‘past due'. (Quora)