Seeking Alpha has an excellent explanation of the current book value for AGNC. I tried to cut and paste but it would not work. Google the following and you will see the article.
AGNC's recent sell-off is overdone and investors are focusing on the wrong risks, says sector expert REIT Analyst. A thorough valuation pegs book value 18% higher than market price.
I think it's a little late to the party to be shorting at this point. The last few days has been mostly panic selling. I am holding and will wait for the dust to settle. I've added a bit at these prices.