How does the Seal Subscriptions app calculate shipping cost?

The shipping cost for auto-charging subscriptions is calculated in the Shopify Checkout, when the customer places the initial order, based on the shipping rates in your shop and the delivery profiles you set in the Seal Subscriptions app. 

In Seal Subscriptions app, you can turn on the functionality which automatically recalculates and updates the shipping cost in subscription after the subscription gets created, products get added/removed, shipping address changes or a product swap occurs. The delivery cost will be calculated based on the shipping rates set in your shop and delivery profiles you set in the Seal Subscriptions app. You can also adjust/edit the delivery cost for each subscription manually in the app. 

Shipping cost for initial recurring invoice subscription orders is calculated only by the shipping rates set in your shop. Shipping cost for every subsequent order in the recurring invoice subscription is always calculated in the checkout based on the shipping rates set up in your shop.