For clarity, let's assume you've just switched to a plan with the rollover data perk:

Any data you don't use that month will roll over to month two. In month two, you will first use the data included in your plan. If you go over this amount, the rollover data from the previous month will then be used. Rolled over data expires at the end of the second month.

Thank you Timo

Does that mean if I have a 10GB per month plan and my 1st month only used 1 GB, then my 2nd month will have 19GB. Then if my 2nd month only used 1GB again then my 3rd month will continue to have 19GB. Then if my 3rd month used 10GB or 19GB, my 4th month will only have 10GB?

Correct.

Thanks for the reply. One last question. The current Bright Friday deals in November 2022 have a free perk of Rollover Data. That Rollover Data perk applies to the 24 months tap meaning it will rollover data for 23 months meaning if I have a 50GB per month plan and I only use 1GB per month in that 24 months period then my 1st month will have 50GB and the 2nd, 3rd, ….24th each month will have 99GB usage?

Also correct.