The debt clock

What this clock is showing

The large number is an estimate. Treasury publishes total public debt outstanding each business day, and that published figure — with the date it applies to — sits directly beneath the clock. Everything the clock adds on top of it is arithmetic: the published figure, plus the average rate of increase over the last twelve months, multiplied by the time since that reading.

That is a projection, and it is worth being clear about what it is not. It is not a live feed from Treasury. Borrowing does not accrue smoothly second by second; it moves in large, lumpy steps as auctions settle and payments clear. On any given day the real figure will be somewhere either side of what the clock reads. The clock conveys scale and direction honestly. It should not be quoted as a number.

If you need a figure to cite, use the published one beneath the clock, and carry its date with it.

Which debt this is

This is the gross figure: everything the federal government owes, including what it owes its own trust funds — chiefly Social Security. It is the measure the statutory debt limit is written against.

It is not the same as debt held by the public, which excludes those intragovernmental holdings and is the more relevant measure for questions about federal borrowing in financial markets. The gap between the two runs to several trillion dollars, so a debt figure quoted without saying which one it is has not told you enough.

What a rising clock does and does not mean

The debt rises in any year the government spends more than it collects. It keeps rising even when the annual deficit falls — a smaller shortfall is still a shortfall, and it still has to be borrowed. The only thing that reduces the total is a surplus.

Two forces set the pace. The deficit adds new borrowing each year. Interest on the existing stock compounds on top of it, and that component moves slowly, as older securities mature and are refinanced at whatever rates prevail at the time.