This question already has an answer here:
I was able to push my effective rating over 4000 before I started the final assault on Earth and received the "Master and Commander" trophy. I then got to just after you are beamed up to the Citadel and saved. Due to some personal issues I didn't get back to the game and now my Readiness rating is down to 60% (which BTW is the worst "feature" of this game). Does anyone know if my effective rating was "locked" in when I started the assault or do I need to grind it back up to 80%?
It's also annoying you can't find this data without being on Normandy. :-(