Reason:

1. For online loans with a loan amount of 8,000, the overdue interest of 5,000 is relatively high. However, we can't judge whether it belongs to usury only from the amount of overdue interest, but also consider factors such as loan interest rate and loan cycle.

2. If the annual interest rate of the loan is below 25% and the loan term is about two and a half years, the overdue interest of 5,000 yuan may be relatively reasonable, although the amount is high.

3. If the annual interest rate of the loan exceeds 25%, or the loan term is short, the overdue interest of 5000 can be recognized as usury.

Summary:

According to the information provided, it is impossible to accurately judge whether it belongs to usury. In addition to the amount of overdue interest, it is also necessary to consider factors such as loan interest rate and loan cycle, and comprehensively evaluate whether it belongs to usury.