The first report of Parliament's chief librarian-turned-temporary budget watchdog, Sonia L'Heureux, pegs the cost to fund infrastructure at existing levels through 2023-24 at $45 billion.
The report says new and renewed funding will provide $42 billion, while unspent program funding from previous fiscal years will add another $6 billion for a total of $48 billion.
"Funding proposed on the Economic Action Plan would cumulatively exceed the baseline amount by $3 billion," the report states.
The PBO says the analysis looked at the five main sources of funding from the original 2007 budget commitments that was to take the infrastructure program to 2013-14 fiscal year. The sources include the gas tax fund to municipalities, the GST rebate for municipalities, the Building Canada program, public-private partnerships and provincial and territorial base funding.
As well, the analysis considered new and additional funding provided for in the most recent March budget.
NDP Finance critic Peggy Nash asked the PBO to look into the costs of maintaining the real purchasing power of federal infrastructure spending through 2023-24.
Nash said the report Thursday shows that the government is using money from delayed projects in their infrastructure spending targets.
"Jim Flaherty is playing a shell game with infrastructure," she said in a statement, saying the Conservatives are budgeting nearly $2 billion less for infrastructure spending next year, and nearly $5.8 billion less over the next five years.
It is the first report under L'Heureux's helm after former budget watchdog Kevin Page ended his five-year-term last month.
Page, the first parliamentary budget officer to be appointed, often butted heads with the government, whether it was over the true cost of the war in Afghanistan or the real price of F-35 fighter jets.