what is a notice of deficiency 
a notice of deficiency is a legal determination by the irs of a taxpayer s tax deficiency it is an official written claim that a taxpayer owes additional income tax and often interest on that amount plus additional penalties it is issued when the irs proposes a change to a tax return because they found that the information reported on a return does not match their records a notice of deficiency is also sometimes referred to as a statutory notice a statutory notice of deficiency or an irs 90 day letter the official name for a notice of deficiency is irs notice cp2319a notice of deficiency and increase in tax tax laws require that the internal revenue service irs issues a notice of deficiency before assessing additional income tax estate tax gift tax and certain excise taxes unless the taxpayer agrees to the additional assessment although the language in the notice of deficiency says that the irs is proposing a change the notice of deficiency is a legal determination of tax deficiency that is presumptively correct 1 