Why I got overdue?

 
Hi Developers. Hope you all doing well.
I did a job that has a deadline of 15 days  and later the customer increases that time by two days and now it is 17 days.
My  execution time was 17 days as well but when the job has closed my overdue project increased I don't know why. Do anyone know why? I tried my best not to get overdue, but here it is.
Reason: