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How to calculate ABV when adding liquor

I will be brewing the all-grain Moonshine Malt Liquor recipe next week. It calls for adding 6-12 oz of white whiskey for a 5 gallon batch. How do you calculate your ABV after you add it? OG is 1057 so I’m assuming it will finish around 5% give or take. I have an 80 proof moonshine to add. I’m thinking there is a formula but haven’t been able to find it. Does anyone know how to do this or where I can find the information?

(XABV) + (YABV2) / (X+Y) = New ABV%

X = Qty of beer
ABV = ABV% of beer
Y = Qty of spirits being added
ABV2 = ABV% of spirits

Note: Proof of Liquor/2 = ABV%

From Here : … f=&t=27073

If you could indulge me and check my math, just to be sure I’m calculating this right…

5 gallons of 5% beer, adding 12 oz of 80 proof. Everything converted to ounces.

640 oz x 5= 3200 + 12oz x 40= 3680 / 652 = 5.6%

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