Notice of Deficiency (90-day letter)

Last reviewed: May 2026

A notice of deficiency is the formal IRS notice that gives you a limited window to challenge proposed tax in U.S. Tax Court before assessment.

Handle this IRS notice

This page explains the proposed-change notice in plain English and points you to the official IRS help pages before you decide how to respond.

Open official IRS deficiency notice page Open appeal rights overview Open review workspace

Because different deficiency letters exist, match the code on your notice to the exact official page before you act.

How this notice usually works

What it usually means

This is a statutory notice of deficiency, often called a 90-day letter.

Why you usually got it

You usually receive a notice of deficiency after the IRS proposes additional tax and is moving toward assessment.

What to do first

Identify the exact code on the notice, note the deadline, compare the proposed changes to your records, and decide how to respond before the window closes.

Time-sensitive note

These notices are deadline-driven. Missing the petition window can remove the pre-assessment Tax Court route.

Who this is for

People looking for a clearer, calmer path through this tax issue.

When to use this page

Use this page when you need a practical next step, not just a definition.

What to gather

Relevant income records
Statements, receipts, or notices
Tax-year-specific forms if needed

Forms that may matter

Forms depend on the page topic

Step-by-step

Use the summary to decide if this page matches your situation.
Gather the records listed here before making a tax decision.
Follow the step-by-step actions and move into the related tool or next page.

Official sources

Sources and authority

Sources 2/2 Good source coverage Updated May 2026

IRS

TaxHackAI Help Center

Authority source

Action plan

Notice response checklist

Use the dashboard to keep the notice, supporting records, and your review steps connected before you answer or pay.

Checklist progress

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This checklist is saved in your browser on this device.

Do first

Identify the exact code on the notice, note the deadline, compare the proposed changes to your records, and decide how to respond before the window closes.

Watch the deadline

These notices are deadline-driven. Missing the petition window can remove the pre-assessment Tax Court route.

Understand the issue

You usually receive a notice of deficiency after the IRS proposes additional tax and is moving toward assessment.

Use these tools

Open official IRS deficiency notice page Open appeal rights overview

Use TaxHackAI

Keep the IRS notice and your records together. Work from the due date and issue code first. Use review to mark anything that still needs proof.

Check authority

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