My router reports Tx Data Packets and Rx Data Packets for my WAN port and it has a standard setting of 1500 for the MTU.
So, if I keep a running total of these packets I can then multiply by 1500 to get the maximum value of the data that has been handled on the WAN port.
That should be the same or close to the data usage recorded by Xfinity.
Am I correct?
That's not what MTU is;
I read your reference about MTU. I think it confirmed my understanding that a 1500 MTU means that each data packet will be limited to 1500 bytes maximum. So if I have my packet counts I can convert to maximum bytes by multiplying by 1500. Doesn't that make sense?