Hi,
Shared D1 SKU is charged hourly ($0.013/hour). For calculation purposes, there are an average of 730 hours each month over the course of a year. If you multiply $0.013 x 730 = $9.49/month
So in effect you are charged per hour, and if your plan exists for a full month this results in average charge per month of $9.49.
Shared D1 SKU has CPU Time (Day) Quota of 240 minutes. This is the amount of time the CPU can be used total each day before the app will be automatically stopped.
It also has a CPU Time (Short) Quota of 3 minutes. This is the total amount of time the CPU can be used in a 5 minute interval.
You may view the above by navigating to Web App in Azure portal - App Service plan - Quotas blade.
Please see article below for more details on App Service quotas and enforcement:
Azure App Service quotas and metrics
https://learn.microsoft.com/en-us/azure/app-service/web-sites-monitor#-quotas
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Thanks.
-TP