Ontario homeowners can expect the value of their property to have risen an average of 18 per cent when they get their new assessments.

Ontario's Municipal Property Assessment Corporation (MPAC) started mailing out notices Tuesday for the first time since 2012, in the Barrie, Brockville and Cornwall areas.

MPAC does the assessments every four years, and says notices for the rest of the province will be sent out over the coming weeks, showing values rose an average of 4.5 per cent in each of the past four years.

MPAC president Antoni Wisniowski told CBC News that values of homes in Toronto and the GTA have outpaced most of the rest of the province and have increased nearly 8 per cent a year.

"Our evaluation of residential properties is based on the sales that are occurring in a community," Wisniowski explained. 

He said several factors determine the value of a property.

"Location drives the value more than anything else," Wisniowski said, adding that square footage, good schools and access to transit are equally important considerations.

When Ontarians receive their notice from MPAC, "they should look at the assessed value and ask themselves this very simple question: 'On January 1st, 2016, would I have been able to sell my property at that value?'

"If the answer is yes, then the assessment is likely accurate," Wisniowski said.

If not, people should contact MPAC, which says it is "committed to working with them to get it right."

With files from Charlsie Agro