This usually means that the IRS has something on file that either was not included in your tax return or something is not matching. This can cause a delay in releasing your refund. Sometimes the IRS corrects it and then releases the refund, or you might get an IRS letter to explain the reason in detail. With more information, you will be able to provide what is needed.
It is also possible that if the IRS corrects a mistake or error, it can change the amount of the refund. This can also cause a delay.
There is no average delay time known but you can also try to contact the IRS to see if they have more information for you. If it's been more than 21 days since your e-filed return was accepted, you can call the IRS directly to check on your refund status.
