Gravity adjustment after primary - abv calculation?

First Post!

Hi all! I've been reading my eyeballs out here for a while, but haven't had reason to post until now.

I have a question regarding ABV calculations after i re-feed my yeast in order to try to bump the ABV/sweetness.

Maybe I should describe what the heck I'm doing first of all...

I'm making an IPA 60 clone
I undershot my target OG by about ten points (hit 1.055 but was shooting for 1.064)
I suspect the reason for this is that I had a low boil, in high humidity, and realized only half a gallon of evaporation during the boil instead of the anticipated 1.5 gallons - so basically the wort was diluted with an extra gallon of water.

So I decided to toss in 1.5 lbs of LME (boiled for ten or 15 minutes) after primary is complete or very near completing (i have not done this yet as primary is still going on)

So my question is how to calculate final ABV

I've got my initial gravity reading, i'll take another before I add the second dose of malt which allows me to calculate ABV at that point then if I take another reading after i've added the malt, then again before bottling can i just add the two totals? or should i just use the first and last readings like normal?

I guess i could do both calculations just to double check - if both are valid that is.

I just thought of another question: would it be best to get the wort off the yeast cake after primary is done, and before i add the LME?

Sorry for the wordiness, but it's a bit of an odd situation i think.

Thanks!

OG*Vol + OG*Vol/Vol1+Vol2

or

55*5+90*1/6=60 or 1.060

I would leave it on the yeast cake for a month or until all fermentation is complete.

m.

thanks!

just to confirm - you're basically saying to calculate the initial gravity using that formula, then just measure the final gravity to calculate total ABV like usual?

Step 1: Take your original gravity reading

In your case you state 1.055 (use just 55)

Step 2: Take your original volume that went into the fermentation tank

5 gallons (we will use this for calcualtions, you should use what you put in there to the closest points. i.e. 5.25 would be 5 gallons 1 quart)

Step 3: Take an OG reading of the LME, DME or whatever you plan to add. You would need 1.090 at 1 gallon to get 6 gallons at 1.060. So we will use 90

Step 4: Plug in the numbers in the formula and you will get your new OG

Step 5: Measure the Final Gravity and calculate it based off of your adjusted OG/SG.

m.

thanks again!