For some Cloudflare subscriptions and services, you will be charged based on how much a feature was used during your previous billing period. This differs from other services, which are a prepaid flat fee for the upcoming month (e.g. plans, page rules, etc).
For example, if your billing date is March 15 and you enable Cloudflare Workers in the dashboard on March 1, your March 15th invoice will include the Rate Limiting charges from March 1-15. The next invoice on April 15 will include charges for Rate Limiting usage between March 16 – April 15.
Please review the product-specific pages for details on pricing and charges: