The President’s budget gets to the lower figure by excluding $4 trillion in likely additional debt by excluding: 

• Additional discretionary spending ($1,545 billion in spending). Health care reform ($595 billion in spending and $583 billion in revenues).
• Additional cap-and-trade outlays and revenues ($821 billion in spending and $214 billion in revenues).
• Extending “expiring” entitlements ($216 billion in spending).
• Net interest expenses resulting from the increased deficit spending ($251 billion in spending).
• More realistic interest rates ($1,328 billion in spending and $65 billion in revenues).

 In reality, the President’s budget agenda would result in: 

• An additional $5 trillion in spending, $1 trillion in revenues, and $4 trillion in deficits over the next decade; Budget deficits adding $13 trillion to the national debt over the next decade; The national debt held by the public surpassing $20 trillion by 2019, reaching nearly 100 percent of gross domestic product (GDP) Annual budget deficits rising to nearly $2 trillion by 2019 Spending surpassing 28 percent of GDP by 2019, shattering the peacetime record set this year; and
• Washington spending more than $37,000 per household in 2019, compared with $25,000 per household in 2008.

 My entire study of the matter appears in “President Obama’s Agenda Would Bring $13 Trillion in Budget Deficits, Not $9 Trillion” can be found here (click pdf for printable version) 

Brian Riedl is Grover M. Hermann Fellow for Federal Budgetary Affairs at The Heritage Foundation