Our guarantee is simple. If the TaxBrain online tax program makes a calculation error in the preparation of your return, TaxBrain will pay for penalties and interest assessed by the IRS as a result of such error. TaxBrain will not pay your additional taxes incurred as a result of such error. Please note that your use of the TaxBrain Online Tax Service is governed by TaxBrain's Terms of Use, which is presented to you at the time you register with TaxBrain.