A "miscalculation" happens when the IRS changes something on your filing, so that the original refund shown on it is now wrong.  You may have made a data entry error, or forgotten to claim some income.  Or claimed the Recovery Rebate Credit when the IRS records show you were already sent the stimulus.

The IRS will be sending you a letter about this; they do not notify TT.

There's no way for TurboTax to know what the miscalculation was. The IRS doesn't share your tax information with us. The IRS should have sent you a letter stating what the miscalculation was. 

• Please see the following information: Understanding Your IRS Notice or Letter