The Eastern part of Ontario (most of Ontario and all the major towns & cities) lie in the Eastern Time Zone , which is 5 hours behind Greenwich Mean Time ( GMT-5 )
The Western part of Ontario, west of 90° W longitude, is in the Central Time Zone , which is 6 hours behind Greenwich Mean time ( GMT-6 ).
Like most provinces in Canada, Daylight Saving Time, is observed in Ontario, where the time is shifted forward by 1 hour, resulting in a 4 hours ( GMT-4 ) and 5 hours ( GMT-5 ) difference behind GMT for the Eastern and Western part of Ontario respectively.
After the Summer months the time is shifted back by 1 hour resulting in the normal time difference behind GMT.
