The short version

Open the notice, identify the tax year and response deadline, and preserve every page. If it is a notice of deficiency, protect the Tax Court petition deadline while addressing the missing return. Filing that return does not extend the petition period. The IRS expressly warns of this in its CP3219N guidance.

Then separate three questions: What returns were required? Is the IRS’s proposed or assessed tax correct? How can an established balance be paid? Resolving one question does not automatically resolve the others. This guide addresses federal individual income tax notices; a state notice or business-tax matter requires its own analysis.

What the law actually says

What an IRS substitute return does, and does not, settle

Internal Revenue Code section 6020(b) authorizes an IRS-prepared return when a required return has not been filed. For an individual non-filer, the IRS may calculate proposed tax from income reported by employers, financial institutions and other payers. That calculation may omit deductions or credits the taxpayer can substantiate.

An IRS substitute return is not a reason to assume there is nothing left to file. The IRS recommends filing your own accurate return even after it has prepared a substitute, so the account can reflect the proper figures. Follow the response destination in your notice and retain the submitted return and delivery evidence. An adjustment depends on the actual facts and processing; a reduction is not guaranteed. IRS past-due return guidance.

Do not confuse an IRS-prepared return with the start of an ordinary assessment limitation period. Section 6501(b)(3) says a section 6020(b) return does not start that period; section 6501(c)(3) permits assessment at any time when no return has been filed. IRC section 6501. A collection deadline after assessment is a separate issue.

How it works in practice

Start with the notice, not a payment proposal

Record the CP or LTR number, notice date, tax year, requested action, response address and every stated deadline. Keep the envelope with the notice. The IRS’s notice lookup guidance explains where to find the identifying number and directs taxpayers to follow the particular notice’s instructions. A request for a return, proposed deficiency and collection notice require different responses.

Build a simple year-by-year record of what was filed, what the IRS appears to have processed and which amounts are disputed. Compare your filing evidence with IRS records rather than assuming either is complete. A tax account transcript shows account data and later changes; a wage and income transcript shows information returns received by the IRS. A verification of non-filing letter only reports that a processed return was not found as of the request date. It does not decide whether filing was legally required. IRS transcript guidance.

This is a response inventory, not an invitation to postpone a deadline until every missing document arrives. Put the urgent notice and the broader filing work on separate tracks.

Hypothetical: one notice, three missing years

Assume an individual has three unfiled federal income tax returns and receives a CP3219N covering one of those years. The notice includes third-party income, while the individual believes documented business expenses are missing. These are invented facts solely to illustrate workflow, not a client result.

The first task is to confirm the notice’s petition deadline and arrange a timely decision about protecting that right. The second is to prepare an accurate return for the noticed year, reconcile the proposed figures and use the notice’s submission instructions. The remaining years get their own filing analysis and work schedule. Sending all three returns together would not, by itself, preserve the court deadline for the noticed year. IRS CP3219N guidance.

Only after the facts support the tax calculation can the individual sensibly compare payment options. The example assumes no particular deduction, reduced balance or relief outcome.

The numbers: deadlines and the six-year policy

These periods are not interchangeable. The first two concern a notice of deficiency; the third is an IRS administrative enforcement policy.

Scroll the table sideways to read all columns, including sources.

Number	What it addresses	What it does not mean
90 days	General period after a notice of deficiency is mailed to petition the Tax Court under IRC 6213(a).	A universal response period for every IRS letter.
150 days	The statutory petition period when the deficiency notice is addressed to a person outside the United States, under IRC 6213(a).	An extra period anyone may request because records are incomplete.
6 years	The normal delinquent-return enforcement period in IRM 5.1.11.7.1; enforcing more or fewer years requires managerial approval under that procedure.	A statute of limitations or blanket permission to leave older required returns unfiled.

Section 6213(a) also contains rules for a final day falling on a weekend or District of Columbia legal holiday, and protects a petition filed by the last date specified in the notice. Have the actual notice and any applicable special deadline rules checked promptly; do not calculate a deadline from an article alone. IRC 6213(a).

Calling the IRS or sending supporting documents is not a Tax Court petition. Even if you believe the matter is settled, the Court’s guidance cautions taxpayers to protect their petition rights when a notice has issued. If court representation is needed, the representative must be admitted to practice before that Court. U.S. Tax Court guidance.

What this means for you

Address filing compliance and payment ability separately

The IRS instructs taxpayers to file required returns even when they cannot pay in full. Lack of payment funds is therefore a reason to assess payment options alongside filing, rather than abandon the return. IRS past-due return guidance.

Eligibility depends on the particular arrangement. For example, an individual’s online long-term payment plan generally requires all required returns to be filed and combined tax, penalties and interest of $50,000 or less. Being outside the online criteria does not necessarily rule out an installment agreement through another application route. IRS payment-plan guidance.

An offer in compromise has separate requirements, including filed required returns, required estimated payments and no open bankruptcy. An employer must also meet the applicable federal deposit requirements. Acceptance depends on the facts, including income, expenses and asset equity. An offer is not a default solution for everyone with missing returns. IRS offer guidance.

A practical response plan therefore tracks current-year payment obligations as well as old returns. It also distinguishes a proposed assessment from tax already assessed. That distinction determines which dispute and collection questions need attention; it should not disappear inside a single total labelled “back taxes.”

How Sheepdog Tax Resolution can help

Request a meeting with a brief description of the notice, its tax year and any upcoming response date. I can evaluate the appropriate administrative tax response within an agreed engagement. Do not send tax returns, Social Security numbers or financial documents through the meeting request or ordinary email; use the firm’s TaxDome portal when invited to upload documents securely. There is no guarantee of any specific outcome. An inquiry does not establish representation or suspend a deadline.

Sources and review date

Primary authorities and IRS procedures linked above were checked on October 26, 2026. The governing tax year’s law, the actual notice and subsequent procedural developments must be considered for an individual matter.

Prepared by Noah Green, CPA, CFE.

Unfiled Tax Returns and an IRS Notice: What to Do First