Experience: Taxes, Immigration, Labor Relations
replied 3 years ago.
Hi and welcome to Just Answer!
I assuming that you are asking about the statute of limitation on assessment .
(a) General rule Except as otherwise provided in this section, the amount of any tax imposed by this title shall be assessed within 3 years after the return was filed (whether or not such return was filed on or after the date prescribed) or, if the tax is payable by stamp, at any time after such tax became due and before the expiration of 3 years after the date on which any part of such tax was paid, and no proceeding in court without assessment for the collection of such tax shall be begun after the expiration of such period. For purposes of this chapter, the term "return" means the return required to be filed by the taxpayer (and does not include a return of any person from whom the taxpayer has received an item of income, gain, loss, deduction. or credit).
The period of limitations is suspended when the person is audited.
(1) General rule The running of the period of limitations provided in section 6501 or 6502 (or section 6229, but only with respect to a deficiency described in paragraph (2)(A) or (3) of section 6230 (a)).  on the making
of assessments or the collection by levy or a proceeding in court, in respect of any deficiency as defined in section 6211 (relating to income, estate, gift and certain excise taxes), shall (after the mailing of a notice under section 6212 (a)) be suspended for the period during which the Secretary is prohibited from making the assessment or from collecting by levy or a proceeding in court (and in any event, if a proceeding in respect of the deficiency is placed on the docket of the Tax Court, until the decision of the Tax Court becomes final), and for 60 days thereafter.
When assessed - there is a different statute of limitation on collection - see here - http://www.law.cornell.edu/uscode/text/26/6502
(a) Length of period Where the assessment of any tax imposed by this title has been made within the period of limitation properly applicable thereto, such tax may be collected by levy or by a proceeding in court, but only if the levy is made or the proceeding begun-
(1) within 10 years after the assessment of the tax, or.
The statute of limitation on assessment is 3 years after the tax return was filed.
It is 6 years - if omitted income is more than 25%.
No statute of limitation if the tax return was not filed or in case of fraud.