They are estimates based on:
The Facts
"President Bush instituted two big tax cuts, one in 2001 and another in 2003. The first was implemented amid rosy predictions of a 10-year, $5.6 trillion surplus; the second was enacted after the economy appeared to stumble after the Sept. 11, 2001, attacks.
When the tax cuts were passed, the nonpartisan Joint Committee on Taxation estimated how much they might reduce revenue: the 2001 tax cuts was pegged at $1.35 trillion over 10 years; the 2003 tax cut was set at $350 billion over 10 years.
Those estimates have never been updated, even as the economy and the budget have moved on.
Here are two ways to look at how the 2001 numbers might be different today.
First, although the JCT has not gone back and rescored the 2001 tax cuts, the committee recently estimated the revenue impact of virtually the same tax cut — the two-year extension negotiated by President Obama and the Congress. For simplicity, and because some elements were changed in other parts of the tax cut, we will focus just on the reductions in individual taxes.
In 2001, the JCT estimated that the tax-rate package would reduce revenues by $115 billion in 2010. In December, the extension of those tax rates in 2012 was estimated to cost $105 billion. (We have to skip 2011 for complicated, technical reasons not worth explaining.)
The $10 billion difference means the cost of the tax rates rose about 5 percent each year. At that trend, the 2001 prediction of the 2012 tax rate package would have been about $126 billion.
In other words, the current estimate of the cost of the 2012 tax rate reductions is 17 percent lower than what would have been predicted under the 2001 methodology.
This shift, however, appears to be largely because of the impact of the recession, which devastated all government revenues. The reduction is less dramatic if you go back all the way to 2001.
To do this, we compared the Congressional Budget Office’s 2001 prediction for the gross domestic product for each fiscal year. Then we looked up the actual GDP, found in the historical records of the White House Budget Office (Table 10.1). It was lower for each year, and we used the resulting ratio to adjust the size of the tax cut for each year. (Generally, the 2001 tax cut was just under or just above 1 percent of GDP.)
Under this method, for most years, the impact was minimal, just a slight reduction. But when the recession hit in 2008, and the GDP turned out to be 10 percent below predictions for three straight years, the cost of the tax cut was reduced by billions of dollars each year.
Over the 10-year period, the overall size of the tax cut dropped about 5 percent, or $65 billion, to $1.285 trillion. Some people might call that a rounding error in the context of a ten-year federal budget."
Revisiting the cost of the Bush tax cuts - The Fact Checker - The Washington Post
You are welcome to provide documentation (not opinion) to refute any of these facts if you can!