Comcast's mobile division is now charging $20 a month extra to watch HD video on unlimited data plans.

Xfinity Mobile's unlimited data plan costs $45 per line per month, but video streams are generally limited to 480p resolution. Comcast yesterday announced a new $20-per-month HD Pass "for an upgrade to HD video resolution on Unlimited lines (720p on phone and 1080p on tablets)." That raises the monthly price to $65.

Xfinity Mobile does offer cheaper options with HD video if you don't need unlimited data. Comcast said it now allows HD streaming on its limited plans, which cost $12 a month for 1GB, $30 for 3GB, and $60 for 10GB. Comcast charges $12 for each additional gigabyte if you go over your limit. Comcast also now offers a "Data Saver" feature to limited-plan customers, which turns off HD streaming in order to reduce data usage.

Xfinity Mobile has been available since 2017 and is only for Comcast home Internet customers. Comcast doesn't operate its own cellular network, so it resells Verizon Wireless service.

Xfinity Mobile started limiting video streams to 480p by default a year ago. Comcast temporarily allowed customers to contact customer service for a free upgrade to 720p video, but the company said that it would eventually start charging extra for that upgrade. The plan to charge extra for HD video was implemented with yesterday's announcement of the new $20 charge.

Limits on unlimited plan

The unlimited data plan isn't really unlimited, even aside from the video limitation. "After 20 GB of monthly data use, speeds are reduced to a maximum of 1.5Mbps download/750kbps upload, determined and applied on a per line basis," Comcast's plan information says. In addition to that, Comcast's unlimited customers may get slower speeds than other customers "in times of congestion," regardless of how much data they use.

Comcast also caps mobile hotspot usage at 600kbps on its unlimited plan. Comcast said its by-the-gig plans allow mobile hotspot usage "at LTE speeds," a nudge to shift customers from unlimited to limited data.

All these limits likely help Comcast save money on its reseller agreement with Verizon. The new $20 HD pass doesn't lift the 1.5Mbps cap for unlimited customers who use more than 20GB, but Comcast says buying the pass does let users "access faster speeds when the network is congested, such as during concerts and sporting events." Basically, this means unlimited customers who pay $20 extra and use less than 20GB a month will get HD video and will not get slower speeds than limited-plan customers during network congestion.

The various speed restrictions do not apply when your phone is connected to a Comcast Wi-Fi hotspot. There are millions of those around the country, and Xfinity Mobile phones can automatically connect to them when in range.