Adjusting OG/FG Math Problem

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Dubya

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Greetings all. I made my first batch of mead recently, a 1 gallon blueberry melomel. I used D-47 yeast (14% tolerance). It started at 1.080 and I racked it into secondary over the weekend. It was at 1.000 after 2 weeks. I plan to let it sit for a few months, but got ahead of myself and decided to back sweeten with .5lbs of honey. Not shocking that I now have some airlock activity. I don't actually mind, but I'm not sure how to adjust my math to know where I'll be ABV-wise. AND...I failed to take a reading after back sweetening since at the time I was thinking my yeast and batch were done. But from what I've read, I gained roughly 17.5 points with the additional honey. Any help wrapping my head around the numbers is greatly appreciated! I'm excited to condition this one for several months and possibly back sweeten again. The sample was rather delicious already!
 

Lampy

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Assume 17 g sugar per 21 g honey. Also assume that this is the only fermentable component.

0.5 lbs honey = 227 g honey

227 g honey * (17/21) = 184 g sugar

184 g sugar in 3.8 L mead = 48 g sugar per L

Looking at this table I would estimate that you did gain somewhere near 17.5 points.
If this all ferments then you will probably add about 2-3% ABV.

I used this "roughly sort-of" method when I was step feeding my cherry-blueberry mead, but I don't really have an easy way to confirm the true ABV. Adding to the problem was the fact that my yeast just kept on eating up sugar, seeming to do just fine even as they got several ABV %'s above the supposed "ABV tolerance" I found online.
 
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