When you add an upgrade option to allow upgrading from a plan to another plan, there are few Prorated options which you can choose which will affect subscription duration and the payment amount of the upgrade subscription. Below, you can see how each options to choose the right option for your need.
For this option, the remaining active duration of the original subscription will be added to the upgrade subscription. For example, if you upgrade to 6 months plans and have 2 months left from original subscription, the upgrade subscription will have duration 8 months (6 months + 2 months).
For this option, the money which subscriber has to pay for the upgrade will be deducted from the money left from the original subscription. The money left from original subscription is calculated base on:
DEDUCTED_AMOUNT = PLAN_PRICE * NUMBER_DAYS_LEFT / SUBSCRITPION_LENGTH_IN_DAYS
For this option, the subscription start date and subscription end date of the upgrade subscription will be same with subscription start date and subscription end date of the original subscription.
AMOUNT = FROM_PLAN_PRICE * NUMBER_DAYS_LEFT / FROM_PLAN_SUBSCRITPION_LENGTH_IN_DAYS
Note that this amount calculation only works for upgrading to one time subscription plan. For recurring plan, the payment amount for upgrade will still be determined by upgrade option price.
AMOUNT = UPGRADE_PLAN_PRICE * NUMBER_DAYS_LEFT / UPGRADE_PLAN_SUBSCRITPION_LENGTH_IN_DAYS
Note that this amount calculation only works for upgrading to one time subscription plan. For recurring plan, the payment amount for upgrade will still be determined by upgrade option price.