For what you describe, there is no strict formula for determining what is a fair settlement offer. Otherwise, all settlement negotiations would be relatively easy once liability is established.
You should consult with your attorney as to what would be reasonable under the circumstances. One informal question you should ask yourself is what would it take to make you feel "whole" again.
DISCLAIMER: Although I am an attorney, absent a signed retention and engagement letter, I am not your attorney. There are no exceptions to this rule. Moreover, you shall not rely on the information I am providing you, as it is only for your general knowledge and educational purposes. Consider it a good first step in your knowledge acquisition, but not legal advice. Indeed, my analysis is based on the extremely limited facts you have given me, and new facts could substantially alter any answer I give.