Simple BIAB Calculator Question

I plan on helping my cousin with his first all grain batch next weekend. We use my kettle and chiller, so this is my "4th" technically speaking. My first two felt like disasters, but my last one (a German Alt), felt like I got everything right.

He's wanting to brew NB's Houblemonstre IIPA (simple, right? :cross: ), so I want to make sure my math, or the BIAB calc's math, is right. The beer calls for 12 lbs of grain, 6oz of hops and 2 lbs of corn sugar make up the additions.

When I punched in the numbers, it's giving me 7.89 gallons of pre-boil wort and ending with 5.5 transfered. That can't be right, or is it? Am I going to lose 1.39 gallons when I transfer to his carboy??

Here's the calculator link:

http://www.simplebiabcalculator.com/

and NB's Houblemonstre is here:

http://www.northernbrewer.com/documentation/allgrain/AG-HoublemonstreTripelIPA.pdf

Thanks for any help and advice.

There is boil off....and the grain will absorb water also. For a one gallon batch, I normally use 2.3 gallons roughly.