As many as you want.

QuickBooks doesn’t perform a physical close of your books. It does a logical close.

Resolution for 'concurrently issue: 'closing the books: How many accounting period (years) can you have open concurrently?' available: Yes.

The concurrently issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the concurrently issue yourself by looking for a resolution described in the article. If it is a complex concurrently issue or you are unable to solve the issue, you may contact us by clicking here or by using other concurrently support options.

For more information about resolving issues related to concurrently in Quickbooks/QBO or to get support for the issue 'closing the books: How many accounting period (years) can you have open concurrently?', click the link below: