how do I calculate my intake of FCP's as a percentage?

Fat Secret's peferences section charts that for you. You have to obtain the kind of info necessary for your goals, however, in order to determine over what period of time and how much fat loss you want to see - then you insert the caloric intake you need to reach your goal. For instance, if you've found 1900 calories per day is that number of calories, that's the number you insert into the preferences section. The book, Good Carbs, Bad Carbs includes percentages FCP of 30,40,30. Most such books maintain Protein at 30% though the FC can vary such as with the Atkins, Turbo-Protein Diet, Zone, Fit for Life, and Lean Body book/s and I only mention those as they are books I've read among others too numerous to recall.

Calculate calories needed for goal weight

http://caloriecount.about.com/cc/calories-goal.php

Was this a one-time measurement, or is it something that happens every day?

If it's one day only, it may just be the margin for error of your scale.