According to Baymard, 35% of ecommerce sites still display delivery information in this form:

Or the even worse:

 

What should you do instead?

Display the expected delivery date. Something like this: You will receive your order on May 27th.

If an exact delivery date is indeterminable, then a range of dates is acceptable though an exact date is always preferable.  

 

Why is displaying the number of days instead of the date wrong?

It’s wrong because you are giving your customers too much work. There are too many elements to factor into delivery calculations. Let’s look at some of them:

 

Why do customers need exact delivery dates?

Exact delivery dates might not super important for stuff like novelty cups but there are multiple instances when an exact delivery date can make or break a sale:

EXAMPLES