# Unused time and Remaining time in Invoices (Prorations)

The subscriptions are billed in a cyclic way. This means that customers that created a subscription (created devices on the platform) will always be billed the same day of the creation.

However, changes to a subscription in the middle of the billing period, such as upgrading or downgrading can result in prorating charges. For example, if a customer upgrades from the Light subscription (1 € per month per device) to the Standard subscription (3 € per month per device), they’re charged prorated amounts for the time spent on each option.

Assuming the change occurred halfway through the billing period, the customer is billed an additional **1 €**: -0.5 € for unused time on the initial price, and 1.5 € for the remaining time on the new price.

The prorated amount is calculated as soon as the API updates the subscription. The current billing period’s start and end times are used to calculate the cost of the subscription before and after the change.


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