Stephen Harper is promising Canadians another tax break if re-elected - in this case a physical fitness tax credit for adults.

Mr. Harper makes the announcement at a campaign stop Sunday. He starts the day in Ottawa before heading to London, Ont. for an afternoon rally.

The Tories are expected to announce this promised measure would not take effect until the federal budget is balanced, which is currently forecast to take place in four years or less.

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The Tories are effectively pledging to extend an existing fitness tax credit for children to all adults - meaning grown-up Canadians would get breaks for gym memberships and other eligible athletic expenses.

It's not clear how much this new tax relief pledge would cost. The existing children's fitness tax credit, which took effect in 2007, allows parents to claim up to $500 per year for eligible fitness expenses incurred for each child under 16 years old.

The current tax break for kids' sports and recreation cost Ottawa about $115-million in foregone tax revenue in 2010, according to the federal Finance Department.

The Conservatives are timing their latest announcement to coincide with the Liberal Party's release of its election platform of promises Sunday.

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The Tories are expected to contrast their promise of more tax relief with a raft of program spending announcements in the Liberal platform.

In the first week of the campaign Mr. Harper promised a tax cut for families with kids, saying if re-elected he would allow parents of children under 18 to share up to $50,000 of income for tax purposes.

This would allow the higher-earning spouse to flow some of their income to their partner who's in a lower tax bracket.

The "family tax cut pledge," the Tories said, would allow as many as 1.8 million households to save on average $1,300 in taxes.

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The income-splitting promise would also not be enacted until Ottawa's books are balanced, Conservatives say.