The Taxpayer filed timely 2002 federal and New Mexico personal income tax returns. Her federal return was subsequently adjusted by the IRS, resulting in additional tax liability. The Taxpayer failed to file an amended New Mexico income tax return within 90 days as required by statute. In 2005, the Taxpayer received a notice from the Department concerning additional tax due as a result of an error on her 2001 income tax return. The Taxpayer then notified the Department that the same error occurred on her 2002 return and asked for information concerning the forms needed to amend her return, as well as payment options. The Department did not reply to these inquiries. In January 2006, the Taxpayer filed an amended 2002 return reporting the additional tax due for that year. The Department assessed her for penalty and interest on her late payment, and the Taxpayer protested, arguing that penalty and interest should be waived beginning with the date she first notified the Department of her underpayment and asked for assistance in filing an amended return. Held: The Department’s failure to respond to the Taxpayer did not affect the accrual of penalty, which reached its maximum of ten percent long before the Taxpayer notified the Department of the error on her 2002 return. Interest is due because the Taxpayer, rather than the state, had the use of her underreported tax funds during the period at issue. Protest denied.