The #1 reason people abandon their carts is “unexpected costs” like shipping. The last thing a customer wants to see is an extra $25 in shipping and processing fees.
When customers are aware of how much they will be paying for shipping and extra fees, there is a greater chance of purchase completion because they aren’t caught off guard. Just make sure you aren’t surprising your customers with fees
Baymard Study on 2016 shows that 24% of online shoppers abandon their purchases because of hidden fees
that are only revealed upon checkout (i.e couldn't see the costs up front)
UPS Pulse of the Online Shopper™ - 2015 Show that 44% of shoppers abandon their cart because they wanted to get an idea of total costs to compare before buying. 22% stop the purchase when they find the store did not clearly mention shipping costs
Event though the app generates the calculator widget as per your theme style, you can customize the widget as you wish.