Calculating ABV after adding exra sugar

[Gerry Nobody]

Ok, a bit of a complicated question here, higher mathematics to me, but then I'm a newbie to wine. I followed a recipe for pumpkin wine which involved adding sugar in three stages over the first couple of weeks. To make a long story short, just after second batch of sugar was added OG was 1.063. After 5 days of fermenting and just before the third and last batch was added OG was 1.031 (ABV at this point 4.2% according to online calculator). OG just after adding third batch was 1.036 and now it embarks on its long journey to god-knows-what it will taste like without any further interference from me.
What I'm wondering is: will I have any way or calculating the final ABV from FG? Is there a way of doing it if you know the initial ABV (just before I added the last of the sugar).
Not a massive big deal but it would be interesting to know...

 

[khannon]

Iirc, 1lb of sugar in 1gal has a sg of 1.040. That should help you do the math. Add to the og side then do the abv math vs fg to get abv.