Shipping charges to multiple addresses are calculated for each address in the checkout as if each were a separate order completed individually.
As your customers proceed through the checkout process, they will see their order broken up into suborders, each with its own associated shipping charge.
These charges are taken directly from your defined shipping rates in Shopify.
You have a free shipping rate set up in Shopify for orders over $75.
The total value of your checkout is $150 and you have 2 shipments in your multi-address checkout, one valued at $50, and the other valued at $100. Only the shipment valued at $100 will qualify for free shipping.
You have 2 weight based shipping rates defined in your store. The first rate is for orders under 10 lbs, and has a cost of $7.50, and the second is for orders over 10 lbs, with a cost of $10.
The total weight of your cart is 15 lbs, and you have 2 shipments in your multi-address checkout. One of the shipments has a weight of 13 lbs, and the other has a weight of 2 lbs.
The 13 pound shipment will have a shipping cost of $10, while the 2 pound shipment will have a cost of $7.50.