Labor's $20 billion shortfall ahead of tonight's federal budget

A leaked federal budget document reveals a $20 billion miscalculation by Labor which is set to deal a "massive blow" to the opposition.

The document highlighted a significant shortfall in the opposition's expected revenue from taxing smokers.

Nine Network political editor Laurie Oakes warned Labor will fall short of fulfilling its spending promises which included fully funding the Gonski school model.

Mr Oakes said the revelation will cause a "headache" for opposition and is a "massive blow" to Bill Shorten's funding promises.

Labor had previously announced its proposal to fund education plans through a big increases to tobacco excise over four stages.

The plan was first announced last year by shadow treasurer Chris Bowen.

Labor stated the excise will raise $47.7 billion in revenue.

Mr Morrison's budget also includes a tobacco excise but will raise just under $28.2 billion, $19.5 billion dollars short of Labor's estimations.

"That's a whopper of a funding hole facing Mr Shorten," Mr Oakes said.

The political editor clarified the disparity was not the Labor party's attempts to "fool anybody".

"Labor had its policies costed by the parliamentary budget office. They're not allowed to use treasury so that's all they can do," he said.

"Things have changed since then. Treasury has a different view."

During a press announcement this morning Mr Morrison continued to spruik the government’s 2016 budget tagline of "jobs and growth".

"The most important thing is that it delivers on economic plans for jobs and growth," he said.