The IRS Statutory Notice of Deficiency is perhaps the most important Tax Notice a taxpayer can receive. It prescribes strict timelines to challenge proposed IRS actions and is a taxpayer’s ticket to Tax Court. If a taxpayer misses the prescribed 90-day deadline to file a Tax Court petition, then he or she gives up significant and substantive rights to challenge the proposed IRS action. It is a hard deadline. However, changes of taxpayer addresses can become important concerning proper notice and the last known address rule. Under this rule, the IRS must notice taxpayers at their last known address; if they do so, they have met their notice requirements. This was the issue in Gregory v. Commissioner (IRS). In that case, the IRS issued a Statutory Notice of Deficiency to the taxpayers at their old home address. For obvious reasons (they no longer lived there), the taxpayers did not respond to the Statutory Notice until it was discovered after the 90-day deadline by their CPA POA. The IRS sought to dismiss their Tax Court case as untimely. However, the taxpayers prevailed because they had put the IRS on notice of their change of address via two forms: IRS Form 2848, Power of Attorney, and IRS Form 4868, Request for Extension of Time. The IRS argued, in part, that the taxpayer failed in this regard because they did not file a Change of Address form, IRS Form 8822. The Court disagreed, holding, in part, that the IRS was “on [reasonable] notice” of the change of address – despite the Form 8822. This is a precautionary tale for two reasons: one, it underscores the supreme importance of the 90-day Statutory Notice of Deficiency timeline and its hard deadline; and two, the extreme importance of putting the IRS on notice of your current home address. This was fact specific case and should not be relied upon as a means to notify the IRS of your change of address. The better practice is to complete an IRS Form 8822, Change of Address.