I recently just read an article on FEDSMITH (?) re retirement/OPM issues and I believe they stated that your interim pay is a % of your annuity however, you do not receive a % of the supplement as interim pay. Your first (full amount) annuity check will include your supplement as well as your full annuity. You will then receive any back pay to catch you up both in annuity and supplemental pay. A friend of mine retired 8/31/2011. His pay was adjudicated 12/31/2011, received full annuity and first supplemental pay. Same date there was a 2nd deposit for the back pay!!! Hope this helps!