Story highlights The White House says their blueprint balances the budget by 2027

The CBO says Trump's budget math overestimated economic growth to the tune of $3.4 trillion

(CNN) When the Congressional Budget Office scored President Trump's budget this week, some of the numbers came out looking different -- very different.

The White House says its blueprint balances the budget over the next decade, reining in the deficit from $603 billion this year to a $16 billion surplus in 2027. But the CBO estimates a $720 billion deficit in 2027 -- and more than double the cumulative deficit over the next 10 years.

So here's the fundamental mismatch: The CBO says Trump's budget math overestimated economic growth to the tune of $3.4 trillion in tax revenue over next decade.

Trump's calculations rest on the assumption that real GDP will increase 3% year-over-year by 2020. But the CBO says not so fast. The nonpartisan agency pegs its estimate around 1.8% -- much closer to the average rate over the last two decades.

"The deficits that CBO estimates would occur under the President's proposals are larger than those estimated by the administration," the report says. "Nearly all of that difference arises because the administration projects higher revenue collections -- stemming mainly from a projection of faster economic growth."

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