# How to determine when a subscription cycles using webhooks

Subscriptions items can cycle at different intervals using the `current_period_start` and `current_period_end` parameters. For example, one item can cycle monthly and another annually. Depending on how you're currently listening to `customer.subscription.updated` webhook events, you may need to update your integration to determine if an event was for a subscription cycling.
### Determine when a subscription cycles
When a subscription cycles to a new billing period, Stripe generates a [customer.subscription.updated](https://docs.stripe.com/api/events/types#event_types-customer.subscription.updated) event. However, not all subscription update events indicate a cycle. To reliably determine if a subscription has cycled, examine specific changes in the event's data.
A subscription has cycled if **all** the following conditions are true in the `customer.subscription.updated` event:
* The event's `previous_attributes` contains a change to the `latest_invoice` field.
* When the `items` array is present in `previous_attributes`, for **each** **item**:
  * The item's `current_period_end` in `previous_attributes` matches its new `current_period_start`.
  * The new `current_period_start` is later than the `current_period_start` in `previous_attributes`.
### Common pitfalls to avoid
* Don't assume all items cycle together.
* Don't only check the first item in the subscription.
* Don't skip checking the `latest_invoice` field.
* Don't rely only on checking if `items` exists in `previous_attributes`.