Four years ago, the Tories pledged to implement the tax credit once the federal budget was brought back into balance.
With the government projecting a surplus this year, Harper has introduced other 2011 promises that were contingent on balancing the books.
They include the controversial $2-billion-per-year income-splitting measure for couples with kids, which was a central pledge in the Tories' 2011 platform.
On top of that, the Harper government doubled the children's fitness tax credit and almost doubled the contribution room for tax-free savings accounts — two measures that were also contingent on a balanced budget.
On Tuesday, Harper was asked about the adult fitness tax credit, a proposal that would allow Canadians to claim up to $500 in eligible fitness registration fees.
"I think we made 107-some commitments in the last election and I can see that is the only one we have not done yet," Harper said at the campaign stop in Quebec City.
"I think that's a pretty good record actually."
Harper said the delay was due to design issues and added that the government is continuing to consult on the plan to ensure the credit accomplishes what they hope it will do.
In their 2011 platform, the Tories estimated the adult fitness tax credit would reduce government revenue by $69 million in its first year of implementation and $275 million the following year.
"It says nothing about the fiscal situation because it's actually a relatively small item," Harper said of the delay.
The Tories tabled a budget in April that projected a $1.4-billion surplus in 2015-16, but the economy has struggled ever since.
Their political opponents say that because of the hobbled economy they don't believe the government is heading for a balanced budget this fiscal year.
Last month, an analysis by the parliamentary budget office cast doubt on the Conservatives' promise to balance the books.
The report said that based on the Bank of Canada's downgraded economic growth forecast, the federal government was actually on track to run a $1-billion deficit in 2015-16.
The economy shrank in the first five months of the year, leaving Canada one month shy of a technical recession.
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