Alerting on Daily Cycle Data

Hello all,
I am trying to set up a Grafana alert to monitor usage over a billing cycle. I have a datasource from Zabbix, which is feeding my daily usage numbers to Grafana - The number increases all day long until resetting at midnight. I need my billing cycle to start in the middle of the month, so I need a way to add up all the values from the 13th of the previous month to the 13th of the present month, based on a number that resets on a daily basis. To make this slightly more challenging, I need to do this in an alert, so that I can know when I am reaching my limit

Can someone advise on how best to configure and set this up?

Alternatively, I do have a live usage per minute that I could calculate on, but again I need it on a rolling 30 day, mid month period. I would prefer not to use this latter data source as it is a less reliable one than the day-to-day stat I get

Do you have all of the daily values being stored somewhere?

Yep, they’re stored for over 30 days

Have you tried your query in Explore with the data source?