Keeping the loyalty of both Miranda and Jack

According to the Mass Effect Wiki it is possible to keep the Loyalty of both Miranda and Jack "if your Paragon or Renegade scores are high enough, you can choose an option favoring neither person and keep the loyalty of both."

How can I determine if my Paragon/Renegade score is sufficient to keep the Loyalty of both characters?

Your Paragon/Renegade score has to be at the level just below Max, however if you alienate one of them you do get another chance to get their loyalty back (anytime before you head through the "main" portal), but then your chosen alignment has to be maxed out.

Short of actually going through the confrontation to see if you get the option, you can't really tell.

Save before doing the second loyalty mission, so you can revert if you have to.