What should be the optimum value of the national debt? (Warning! Answer needs arithmetic!)?

The correct answer is $26T. The national debt should be at least $8T more than it is.

Every federal dollar spent and not repossessed by the IRS is saved by the private sector. Not counting bank debt and assuming that, over the long haul, trade is balanced, the national debt is equal to the total accumulated savings of the private sector, to the penny. There is no other legal source of savings.

If the average American retires at 65, survives 15 years (180 months), and needs $1,800 monthly (current average income of 27 million SS beneficiaries*) to live decently (?), that comes to 180 x $1.8K = $324k in savings needed by each retiring person. The average savings at the halfway point to heaven or hell are $162K. For the entire 27 million retirees, that comes to $4.4T in current savings.

To save $324K over 40 working years, an individual will have to save on average $8,1K annually. At the halfway point, she should have $162K. Allowing for the fact that she will do most of her savings after the midpoint, let’s divide that by 2 to arrive at an average midpoint savings of $81K. For 270 million working individuals, that comes to almost $21.8T required savings for the working community.

For the entire population of adults, the required savings is over $26T. That is the optimum national debt assuming no accumulated trade deficit.

* http://www.ssa.gov/pressoffice/basicfact.htm