You can find out more about Comcast's usage plans (data caps) here: https://www.xfinity.com/support/internet/data-usage-plan/
This guide is meant to help you understand some basics about data usage.
The Comcast usage meter
If you are the primary or self-managed secondary account holder, you can view your current usage and usage history by signing in to your Usage Meter page. You will need to enter your XFINITY username and password.
You can also download the Xfinity Usage Meter Desktop Application
If you are interested in a technical survey of the meter's accuracy you may want to read the report by NetForcast. (pdf file)
Your data consumption
Streaming video commonly uses the most data for many households. Streaming HD content uses around 3 GB per hour while streaming 4K content uses about 7 GB an hour. Some services like Netflix allow you to adjust video quality to reduce data consumption.
Activities like torrenting, large game downloads, video conferencing and uploading can also use significant data.
Other activities like gaming, web surfing, VoIP services, music, and email communication don't typically consume large amounts of data.
The Comcast data calculator may help you estimate your usage.
Keep in mind that the meter is not in real time, there is a lag between a traffic event and when the meter will actually display it. Also, the meter operates on universal time (UT or GMT). This means that the "new month" which will show a meter reset to zero appears in the evening of the last day of the month across the US. For example, Eastern Time is typically 5 hours behind UT or GMT. (Source: NetForcast report)
You may be interested in NetForcast's Third Accuracy Assesment of Comcast's Internet Usage Meter. (pdf)
A good way to test the usage meter is to schedule a period of "digital silence". Power your network equipment completely off and monitor the usage meter. If the meter still shows usage, then there is a problem outside of your control. If it shows no usage, then you can concentrate on resolving the issue on your network.
If you see a large discrepancy between your estimated usage and the Comcast meter:
1) Make sure to run a virus scan and a malware/adware scan on all of your computers. These types of programs can run in the background and even turn your computers into zombie machines.
2) Secure your WI-Fi network! Make sure your neighbor isn't leaching off of your account and consuming your data. If you need help with this, the folks in the networking forum would be happy to help you.
3) Contact Comcast's Customer Security Assurance Team: 1-888-565-4329, 6:00am - 2:00am EST, 7 days a week. They may able to help you figure out why your usage is not what you expect.
*** FYI: If you exceed your data threshold, Comcast DOES NOT THROTTLE your speeds. ***
Last updated 4/06/17