Adjusting Alc% with Whiskey Added to beer

[TaylorBrewed]

Hi all, I plan on making a Irish Car Bomb Stout tomorrow and wondering how I would go about adjusting or figuring out the alcohol percent when it is finished? The recipe calls for adding 12oz of Jamison Irish Whiskey(40 proof) to the secondary. Looking at the notes of a family friend who made this back in March shows a OG of 1.050 and a FG of 1.013 for 4.86%Alc but think by adding the Jamison to the beer it would increase the alcohol percent. He is out of country on vacation right now so I cant ask if he took his final gravity before moving to the secondary. He shows he kept the beer in the primary for 2 weeks before moving to secondary for 2 weeks and adding the Jamison. So how would all of you figure this out? Any help would be greatly appreciated.

 

[stpug]

It's actually 80 proof or 40% alcohol by volume.

12oz*80proof = 640oz*x
x=(12*80)/640
x=1.5 proof or 0.75% alcohol increase in 5 gallons (i.e. 640oz)

4.86% + 0.75% = 5.61% ABV Irish Car Bomb Stout

 

[TaylorBrewed]

Sorry 80proof = 40% .

Anyways this is what I came up with
I's just using a 375ml bottle of Jamison which is equal to 12.7oz
40% alcohol of 12.7oz =5.08oz
I Make 5 gallon batches which = 640oz
5.08oz divided by (640oz +12.7oz) = .77 percent alcohol added to my batch of beer.

Did I do this correct?

 

[TaylorBrewed]

ahhh thanks bud you beat me to my post.