Why shipping needs its own math
Many sellers compare only the label cost to the shipping amount paid by the buyer. That misses the envelope or box, protective material, label paper, tape, the time spent packing, and the occasional return or replacement shipment. On a single order, these costs look small. Across hundreds of orders, they can become the difference between a product worth restocking and one that only creates work.
The calculator turns packing time into a labor cost so you can see the real cost of fulfillment. This does not mean every seller should charge buyers separately for labor. It simply makes the cost visible before you choose free shipping, paid shipping, or a higher item price.