How long does croup last?

Common cold. Since it generally caused by cold viruses, it may last 1-2 weeks, just like the common cold. Usually the first night or 2 are the worst.
3-5 days. However a little longer or shorter would not be concerning. If your child is not improving, or certainly seems to be worsening, they need to be rechecked right away.
5-7 days. Croup usually lasts 5-7 days the first 2 days are the most severe. The barking cough is worse at night and when a child is crying or upset.