How we can preview prorations in laravel cashier or what is the logic of calculating prorations on any subscription?

I have created a subscription for any of product using laravel cashier and the subscription is for one month then in id of subscription user wants to sowngrade or upgrade his subscription then how can we calculate unused time on cost on existing subscription in laravel cashier.

I am not using stripe/stripe-php i am using laravel cashier

How we can preview prorations?or What is the logic of calculationg prorations?

via Chebli Mohamed