There's a link near the bottom of the page where you can check by Zip code and some links where you can log into your account and check.
When you log into your account and view your Data Usage Overview under the heading of Devices, there's a link to set up "alerts" regarding your usage. The default is 90%, 100% (mandatory), 110% and 125%.
Edit-- My original post stated the cost of Instant TV is $20. That is incorrect. The new price effective for many as of Jan 2019 is $12. This includes locals, any of which in HD available, and the current "broadcast tv fee" (varies by market) which went from $7.75-$10,) DVR Lite (20 hrs) Music Choice channels with Showtime & Starz included for 1 yr. Then they increase to $5 per month. Optional others available of course for a fee. Just a clarification.
harshness, fully agree. As a SECOND EDIT:-( , Comcast has informed Instant TV customers it has added $10 for the "broadcast tv fee." Their deception lies in the "bundle." If you bundle internet and regular tv service, while on the bill there is the bundled price, and the line items of fees and taxes, it does not show what is paid for the internet & tv service seperately. However, Instant TV is shown as a seperate line item since it is considered an add on..That being said, they desperately try to show "savings for the month.." I do know I have the Blast (150Mbps down) on promo 1 yr for $49.99. I could go a step further and save $13.00 with my own modem router or gateway. That seems to be where the savings really would kick in. Finally, Comcast is allowing customers to purchase their own equipment to go with Instant TV, not to mention keeping video sub numbers inflated, and hoping you will want to subscribe to other premium services beyond what is free for 1 yr, Showtime and Starz. Their "DVR Lite" is a crappy 20hrs..fills up fast even in SD programming. This is based on a 30min SD show, (sitcom) and will hold approx. only 35 or so episodes before full.