Prime Minister Harper is promising a tax break for two-parent families -- although they'll have to wait for it until the federal government eliminates the deficit.

The 2.5 billion-dollar scheme would allow spouses with children under the age of 18 to split household income up to 50-thousand dollars in order fall into lower tax brackets.

The plan wouldn't begin until 2015-16 under current Conservative deficit projections.

Harper calls it a "major, structural tax reduction" that would affect 1.8 million Canadian households.

The Conservatives say the tax cut would average $1,300 per family but economists say the actual dollar value varies widely.

Frances Woolley of Carleton University says the biggest beneficiaries would be higher earning, single-income households with a stay-at-home spouse.

He says someone earning more than $127,000 a year with a stay-at-home spouse would save more than six-thousand dollars.

A one- or two-income family in which the highest earner makes less than $40,000 would get nothing.

The Liberals and NDP are already criticizing Harper for announcing a plan so far into the future.

But he says he wanted to let Canadians know his fiscal priorities once the federal books are balanced.