How to collect daily and monthly bandwidth consumption

I am on Comcast and they have a monthly 1TB bandwidth cap at which point I have to pay. I’m interested in adding two panels, backed by Prometheus, to my dashboard. The first is bandwidth used today, resetting every day at midnight. The second is bandwidth used this month so far, resetting every month. I’ve struggled to get a query which seems to work. Prometheus is polling SNMP from my router and I’m currently using ifInOctets and ifOutOctets.

Thank you!