To define your fiscal year, go to the menu Accounting > Configuration > Periods and click Fiscal Years. Now click the Create button and fill the top 4 fields of the form: the name of the fiscal year, the code and the start and end date. Save and click the Create Monthly Periods or Create 3 Months Periods button. The periods will now be created for you according to the start and end date of your fiscal year. Of course, you can also create periods manually instead of using the Create buttons.

When you use the Create Monthly Periods or Create 3 Months Periods button, Odoo also creates an opening period to allow you to post your outstanding balances from the previous fiscal year. Notice the Opening/Closing Period checkbox to indicate such a period.

If you want to define long-term budgets, you can also create several years in advance. Make sure, however, that fiscal years and periods cannot overlap.

It is also possible to extend or shorten your fiscal year if your company decides to do so during the year. Just remove the unused periods from the financial year and change the end date of the fiscal year. To extend the duration, change the end date and add more periods manually.