> ## Documentation Index
> Fetch the complete documentation index at: https://help.the-meridian.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Billing interval

The billing interval is how often a plan charges. Offering an annual option alongside monthly helps merchants pick what fits them and brings your app more predictable, up-front revenue.

## Monthly and annual pricing

Each plan sets a **monthly price**, and can optionally add a **yearly price**. When a plan offers both, the merchant chooses the cycle on the [pricing page](/plans) at checkout. The interval isn't fixed on the plan, it's the merchant's choice.

* A **monthly price is required**; a **yearly price is optional**.
* Offering yearly requires a monthly price too.
* A plan with usage-based [events](/introduction-6) is monthly only: Shopify bills usage on a monthly cycle, so it can't be sold annually.


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