If financial year runs for more than 12 months, quickbooks automatically takes care of this?

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You will have to complete the year-end tasks in QuickBooks Online. This is to prepare your books for the new year. You'll want to check out the guides in this article to end the year smoothly: QuickBooks Online year-end guide and checklist.

When it's time to close the books, you can follow these steps:

1. Go to the Gear > Accounts and Settings.
2. On the left panel, click the Advanced tab.
3. In the Accounting section, put a check mark on the Close the books box.
4. Enter a closing date. Give yourself a comfortable deadline. You shouldn't need to edit any transactions before this date. Your new bookkeeping work will start after this point.
5. Select the Allow changes after viewing a warning and entering a password option from the drop-down menu if you want to require a password before editing your closed books.
6. Hit Save and then Done.

Please see this sample screenshot for a visual guide:

I'm also adding this article for more details: Close your books in QuickBooks Online.

I'll be around if there's anything else you need help with your QuickBooks Online account. Take care!