Hi,
A fiscal period is the time covered from the day your business starts its business year to the day your business ends its business year.
For an existing business, the fiscal period is usually 12 months. A fiscal period cannot be longer than 12 months. However, it can be shorter than 12 months in some cases, such as when a new business starts or when a business stops.
Self-employed individuals generally have to use a December 31 year-end. If you are an eligible individual, you may be able to use an alternative method of reporting your business income that allows you to keep a fiscal period that does not end on December 31.
To know more details -
https://turbotax.intuit.ca/tax-resources/business-owner-tax/establishing-fiscal-year-for-your-busine...
Hope this helps
Thanks
