Should you provide an option to calculate shipping in the cart page?

If you ship to multiple countries or your shipping charges differ for different locations within the same country, then you definitely have to allow your customers to choose the shipping location or specify the zip code in the cart page so that they can calculate the shipping charges before proceeding to checkout. A simple pop-up that takes location input and a calculate button. If the user has already logged in, then fill the location with the default delivery address.