Ontario's financial watchdog says there is a "significant risk" the Progressive Conservative government's spending plan will fall $5 billion short of what's needed for health and education.

Financial Accountability Officer Peter Weltman says in his economic outlook and budget report released today that the need for those services will far exceed what's in the government's fiscal plan by 2021-22.

He says the government could balance the budget by that year, instead of its target of 2023-24, if it doesn't implement tax cuts that were promised during the election but haven't yet been implemented.

Weltman says the government has introduced many program and policy changes intended to cut costs over the past 18 months, which he estimates will save $6.6 billion.

Even after factoring in those cost-saving measures, Weltman says the demand for public services will be $4.8 billion higher.

He says if the government doesn't plan to boost spending by $5 billion, it could make additional cuts, look for more efficiencies in the delivery of public services, or underfund current programs.