The federal government incurred a deficit of $90 billion in the first four months of fiscal year 2008, CBO estimates, about $48 billion more than the shortfall in the same period last year. Shifts in the timing of certain payments and receipts account for about one-third of that increase in the deficit. ... The federal government recorded a surplus of $15 billion in January, CBO estimates, less than half the surplus recorded in the same month last year. Noteworthy is the reason for the uptick in spending: "Spending for net interest on the public debt accounted for the greatest growth, up by about $5 billion (or 30 percent)." CBO: Monthly Budget Review