HBO subscription: what is meant by cost "per month"?

[Slowbutsteady]

Can't find anywhere how the cost "per month" is defined.
If I start and HBO subscription today with two days left in December will I be billed $15 for December?
Current wait time to call HBO is 45 min and googling this led nowhere. And of course nothing in the FAQ.
Anyone?

 

[-Gonzo-]

It’s means if you start a subscription today you won’t be charged until the 30th of next month.

 

[babens]

I'll also add that if you purchase it as an add on through another service, such as Hulu, that it will prorate the cost until you reach your next billing date for that service. So if your Hulu gets charged on January 13th and you add on HBO Max today, December 30th, then it will initially charge you $7.50 and then add the full $15 to your charge on the 13th for the next month.

 

[Audit13]

If you have a discount Hulu plan like me @ $1.99 per month, adding HBOMax through Hulu causes me to lose the $1.99/month promo price so I will subscribe directly at $14.99/month.