How does the Gran class fee work?

Hello, I have a JR Green Car pass (before typing, yes I know this does not cover the Gran Class) and I want to know if paying the Gran Class I have to pay the entire fee or will the green car pass cover a portion of it. According to Japan-rail-pass . com, it says that "Cars accessible with additional charge" under GranClass. But I don't know how dated this info is, so I'd rather be disappointed now than at my trip. I intend to travel from Tokyo station to Utsunomiya and back.

Thanks

From the official JR Pass site (i.e., not a reseller/intermediary):

"If you use the GranClass car, only the basic fare is covered with your JAPAN RAIL PASS for both Green Car and Ordinary Cars and you must pay the limited express charge and the GranClass car surcharge additionally"

http://www.japanrailpass.net/en/about_jrp.html#bm_004

From my own experience, though a different scenario: I booked a private room on the Sunrise Izumo sleeper train using a Green JR Pass. The base fare was fully covered, but I had to pay an extra JPY 16,970 for the express surcharge and accommodation fee.

Cheers.

PASS Web mentioned.
http://www.japanrailpass.net/en/about_jrp.html#bm_004
------------------------------------------------
*4 If you use the GranClass car,
only the basic fare is covered
with your JAPAN RAIL PASS for both Green Car and Ordinary Cars
and you must pay the limited express charge (as reserved seat)
and the GranClass car surcharge additionally.
------------------------------------------------
"Basic(Base) fare" means "railway section fee" fr A to B stn.
Tokyo to Utsunomiya : 1940Y/oneway adult

(note)
All "Hayabusa(solo also with Komachi both) " and "Hayate" won't be stop Utsunomiya.
So you must book "Yamabiko(with Tsubasa or not)" or "Nasuno" by E5/H5/E6 series car.
https://en.wikipedia.org/wiki/Yamabiko
https://en.wikipedia.org/wiki/Nasuno
http://www.jreast.co.jp/train/shinkan/tohoku.html
BC Some trains using "E2/E3" series(car type) no GranClass cars.
Also if by "E5/H5/E6" series with GranClass
however,some trains no GranClass attendant service(fare discont).
No GranClass attendant service : 2470 + 5150 = 7620Y plus
with GranClass attendant service : 2470 + 7200 = 9670Y plus

Use HyperDia.
http://www.hyperdia.com/en/cgi/en/search.html?dep_node=TOKYO&arv_node=...
Change dep date/time at page bottom first
then change seat fee pull down menu to "Gran Class".


BUT,
no need for short ride(about 100km a bit over/under 60min) worthless except if really super crazy railfan you are.
Also train speed won't be speed 320km/h max only 275km/h max in short time.