The CBO estimates the debt will be at $US16.5 trillion in two years, or 100.6 per cent of GDP.
But these numbers are incomplete.
They do not count off-budget obligations such as required spending for Social Security and Medicare, whose programs represent a balloon payment for the Government as more Americans retire and collect benefits.
In the case of Social Security, beginning in 2016, the US Government will be paying out more than it is collecting in taxes.
Without basic measures - such as payment cuts or higher payroll taxes - the system could be on the road to bankruptcy, according to officials.
"Without changes," wrote Social Security Commissioner Michael Astrue, "by 2037 the Social Security Trust Fund will be exhausted. There will be enough money only to pay about $US0.76 for each dollar of benefits."
Mr Kotlikoff and Mr Moylan agree US national debt is much more than the official $US13.4 trillion number, but they disagree over how to add up the exact number.
Mr Kotlikoff says the debt is actually $US200 trillion.