It doesn't calculate XPs at all.

And it's a very cumbersome way to multiply your fare by 4/6/7/8 just to see how many Flying Blue miles you'll earn....when this is already shown in your booking online once you've made it. Maybe if you've already got into the habit of trying to figure out how many Skypesos you earn that muscle memory means you're more likely to go here than to the Flying Blue tool; but the FB tool is quicker and easier for figuring out what the XPs are (most frequent flyers will already know the earning for their usual routes, and therefore for all comparable routes)